Until about five years ago, the Global Positioning System (GPS) existed in the realm of high-tech military thrillers. Fictional spies would tote hand-held units that precisely displayed their locations (or that of their objectives) anywhere on earth - with street maps and 3D topographic representations to boot! Reality imitates artShow full article

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Until about five years ago, the Global Positioning System (GPS) existed in the realm of high-tech military thrillers. Fictional spies would tote hand-held units that precisely displayed their locations (or that of their objectives) anywhere on earth - with street maps and 3D topographic representations to boot!

Reality imitates art. In the past ten years, three amazing things have happened. First, the U.S. military opened up the Global Positioning System for civilian use. Then, the price of receivers plummeted from the $1,000-$10,000 range to $100-$200, making them widely affordable. And last, advanced computer-controllable units have appeared, making integration with personal computers a reality. With your Macintosh and about $300 in additional hardware and software, you can do things that were science fiction just a little while ago.

In this article, I explain the technology behind the Global Positioning System and discuss some receiver units currently available. Later in this issue, TidBITS Managing Editor Jeff Carlson talks about GPS technology from a user's perspective, and reviews GPSy, a GPS communications software package I developed for the Macintosh.

Your Tax Dollars at Work -- The Global Positioning System is truly amazing. Developed by the U.S. military at a cost of several billion dollars, GPS is based on 24 orbiting satellites (space-heads call them SVs, which is short for "Space Vehicles"). These satellites broadcast a precise data signal that allow GPS receivers to locate themselves anywhere on the planet. A receiver can calculate its position (latitude and longitude), altitude, velocity, heading, and precise time of day. Most units also have a built-in mapping feature that displays their positions relative to waypoints you've pre-programmed into them and a plot trail that shows where you've travelled. Advanced models have built-in street or waterway maps, plus serial ports for computer connections.

Military and high-end survey-grade models are accurate to the millimeter level (less than one-sixteenth of an inch). However, standard over-the-counter civilian models are nominally accurate to "only" about 100 meters (roughly a city block). This is due to military-induced Selective Availability - a euphemism for scrambling the GPS signal just enough to reduce the accuracy to sub-military levels. Such scrambling leaves the signal accurate enough to find your favorite fishing hole, but prevents you from accurately dropping a cruise missile into the government's classified Area 51 base in Nevada. One amusing consequence is that many car navigation systems that use GPS will put you slightly off the road - making it seem as though you're driving into a river or building!

If you need better accuracy than 100 meters, an FM radio receiver called a Differential GPS unit (DGPS) used in conjunction with your GPS receiver can provide three to ten meter accuracy. The U.S. Coast Guard broadcasts DGPS signals for free along the entire coastline of the United States, and inland for a small subscription cost from various DGPS broadcast companies. The inland cost should go away soon because the Federal Aviation Administration (FAA) wants to use GPS for all aircraft and plans to begin wide-scale broadcasting of free DGPS signals around the year 2000. DGPS receivers currently go for about $500, but once the FAA plan goes into action GPS units should start to have built-in DGPS receivers.

Behind the Scenes -- The 24 satellites have a staggered orbit designed so four satellites will be visible from any location on earth 95 percent of the time. This number four is important, as we will see.

Each satellite broadcasts a repeating message, indicating the position and orbital parameters of itself and the other satellites (almanac), a bill of health for the satellites (health bit), and the precise atomic time. The information is encrypted into a signal with strict timing characteristics.

In order to understand how the GPS system works, we're going to jump into a bit of simple algebra. Remember echolocation from high school physics? If we send out a pulse of sound or radio waves and wait for them to bounce off something and come back, we can determine the distance to the object by dividing the time it took for the reply by the speed of sound (or light).

Distance = Speed * Time
Time = Distance / Speed

GPS works on much the same principle, except that unlike RADAR/SONAR, where the transmitter is also the receiver of the signal, GPS satellites only transmit the timing data pulses; GPS receiver units only receive.

So how does the system work? Imagine you and a friend had precision-synchronized watches and were standing in a football field. If she shouted, "I'm at the far right cornerpost and it's now 5:00 and 0.0000 seconds!" and you heard this message at 5:00 and 0.333 seconds, you could determine how far away she was by the timing delay of 0.333 seconds. Estimating the speed of sound at around 300 meters per second, you can guess she's about 100 meters away from you (or that you're 100 meters away from the far right cornerpost).

Suppose you had another friend at the far left cornerpost and he shouted the same message at the same time and you calculated him to be 150 meters away. Could you tell where you were? Pretty much. You know that you're 100 meters away from your first friend, so you could take a diagram of the field and draw a circle with a 100 meter radius around her known position. Then you could draw a circle with a 150 meter radius around your second friend's known position. The two circles should intersect at two points - one of which should be your real position. With three friends, you'd have no ambiguity.

Draw this on a piece of paper if it doesn't make sense as a written example.

Shouting from the Stars -- The Global Positioning System works on this principle, although it uses much more precise clocks and the speed of light. There's a hitch, though. The above example required that each person had precision-synchronized clocks. If each GPS unit had to have an atomic clock, it would be outrageously expensive. With three friends (or three satellites) we can solve three of these four variables:

X, Y = horizontal position
Z = altitude
t = time

With only three satellites and an imprecise clock, we have to assume altitude to be a known constant (e.g., sea level), since we can only solve for three variables using three satellites: X, Y, and time. But if we have four visible satellites, we can solve for all four variables: X (longitude), Y (latitude), Z (altitude), and t (precision time). The pleasant side effect is that not only do we have our precision location, but we also have precision time - which makes GPS valuable technology not only for geophiles, but chronophiles as well. Many people are now synchronizing their systems or network clocks to GPS signals, since it's a cheap and highly accurate source.

However, thinking back to our example, there are some important caveats. Our friends, or the satellites, must be spaced well apart. If they're too close together, the timing difference between their signals isn't enough to calculate our location precisely. In GPS parlance, this is your "dilution of precision," and it greatly affects your accuracy. Also, there must be a clear path between us and them - we can't have anything blocking our signals, or a large reflective object causing unwanted echoes ("multipath" signals). These errors can further degrade the accuracy of our location.

GPS signals work in the microwave band. They can pass through glass, but are absorbed by water molecules (wood, heavy foliage) and reflect off concrete, steel, and rock. This means that GPS units have trouble operating in rain forests, urban jungles, deep canyons, inside automobiles and boats, and in heavy snowfall - among other things. These environmental obstacles degrade positional accuracy or make it impossible to get a fix on your location.

GPS Receiver Technology -- The core of GPS receivers come in two major variations: sequential single-channel and parallel multi-channel. Single-channel GPS units have only one radio receiver unit, and they must step sequentially through all possible satellites. This takes time and degrades their accuracy, since they may lose a "lock" each time they switch channels. Parallel units have from between four and twelve receivers, each dedicated to one particular satellite signal, so strong locks can be maintained on all the satellites.

There are some two-channel units out there, but in practice these are only slightly better than single-channel units. Parallel-channel units are up to 15 times faster in satellite acquisition times and they are unparalleled (sorry for the pun) in their ability to lock onto the satellite signals even in difficult situations like heavy foliage or urban skyscraper canyons.

Boaters, however, may be content with single or dual channel sequential units, since there are few environmental obstacles on the open ocean. These models are now considered outmoded technology, so you may be able to pick one up cheaply. But for others, don't settle for anything less than a full 12-channel parallel system, especially since the price differential has closed greatly in the past six months.

Reviewing Some Receivers -- Let's take a quick peek at a few low-end consumer GPS units in the $150 to $300 range. All these units have parallel 12-channel receivers. They also all have the same 100 meter accuracy, because the U.S. government reduces all civilian GPS units in a similar fashion. If the government were to remove the SA interference, the units would be accurate to about 15 meters.

If you're shopping for a unit, pay attention to features like form factor (handheld versus mounted); external antennas; mapping, and computer-controllability.

I've included on my Web site a list of resellers where you can buy these GPS units. For local shopping, try your neighborhood boating stores or outdoor sports stores, they often carry the lower-end units.

<http://www.gpsy.com/gpsinfo/ index.html#resellers>

Garmin -- My favorite GPS receivers are from Garmin, Inc. Their main handheld unit, the Garmin GPS 12XL, is about $250. The 12XL is designed for handheld use and fits in your palm. It runs on 4 AA batteries for about 12 hours and has a backlight for night use. Garmin also sells the lower-end GPS 12, a 12XL without an external antenna connection or audible beeper for less than $200, but otherwise sporting the same handheld form factor.

The GPS II+, on the other hand, is designed for vehicular use and sits on a dashboard or console. It has dedicated zoom buttons which make it easier for one-handed use while piloting (though not recommended while driving). Garmin also sells a nifty handlebar mount. I have an older GPS II mounted on my Honda CX500 Custom motorcycle and it's my constant companion when I tour New England. The II+ has a battery life of around twenty hours on four AAs.

The greatest thing about Garmin units is that they have a bidirectional serial port that allows them to hook up to your computer. Though many GPS units can only transmit their current positional information, the Garmin units also allow you to transfer their waypoint databases, route tables, and other useful information. The wide availability of programs supporting the Garmin transfer protocol makes the Garmin units good choices for computer-based use.

<http://www.garmin.com/>

Eagle -- Eagle/Lowrance sells an inexpensive twelve-channel unit called the Eagle Explorer (approximately $200). The Explorer has a strong 12-channel GPS receiver, but unfortunately the user interface is harder to use than the Garmins. The unit also lacks an external antenna connection, which makes it more difficult to use inside vehicles. Eagle/Lowrance units have a proprietary data transfer protocol that's not currently supported in any Macintosh products. I personally wouldn't recommend that you buy a Eagle Explorer. It's too difficult to use either by itself or with a computer.

If you're into boating, Eagle also has a four-channel unit called the Accunav Sport, which has the ability to support plug-in map modules for coastal waterways. It's a nice unit, but the receiver technology is two years old and a bit dated. Shop around for better deals.

<http://www.eaglegps.com/>

DeLorme -- DeLorme Mapping publishes CD-ROM and paper maps of the United States. Their most famous product is Street Atlas, a street level map of the entire U.S. on CD-ROM. But they also manufacture a neat little 12-channel unit called the DeLorme Tripmate. The Tripmate has no display or controls of its own and is designed strictly to be used with a computer. That said, it's a remarkable unit with good performance - and a reasonable $150 price tag.

<http://www.delorme.com/>

Data Cables -- The biggest problem facing Macintosh GPS users is the unavailability of data cables. Most data cables come in PC-style DB-9 connectors, not the Macintosh-style DIN-8. Currently, the only commercial source for GPS cables for the Macintosh appears to be my company. However, you can make your own cables if you're handy with a soldering iron or wire-crimps. My GPS Cable Page provides details.

<http://www.gpsy.com/cables.html>

Finding Your Way -- GPS receivers aren't yet standard equipment in cars, but with price drops and improvements, it's only a matter of time. Ubiquitous availability of GPS devices will help eliminate the angst of finding yourself, in at least one sense.

For more information about GPS, check out resources from the U.S. Coast Guard, NOAA (National Oceanic and Atmospheric Administration), Iowa State University, and my own Web site.

<http://www.navcen.uscg.mil/>
<http://www.ngs.noaa.gov/GPS/GPS.html>
<http://www.cnde.iastate.edu/gps.html>
<http://www.gpsy.com/gpsinfo/>

[Karen Nakamura founded Global Mapping Systems, a Mac-centric mapping and GPS/GIS software development company. Her "other" day job is as a sociocultural anthropologist studying deaf social movements in Japan and United States.]

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Karen Nakamura, who wrote the GPS overview article in this issue, contacted TidBITS with an interesting proposition: Would we be interested in testing some GPS units in tandem with her software, GPSy? Although none of us on staff have a good reason to use a GPS unit in the near future, we were tantalized by three factors: the futuristic ability to pinpoint one's position on Earth using orbiting satellites, the fact that Karen offered to write an article about a subject that interested us, and the chance to play with cool toys. Preparing to Race Satellites -- Karen shipped us a copy of GPSy and DeLorme's Street Atlas 3.0, along with two GPS units, a Garmin GPS 12XL and a DeLorme TripMateShow full article

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Karen Nakamura, who wrote the GPS overview article in this issue, contacted TidBITS with an interesting proposition: Would we be interested in testing some GPS units in tandem with her software, GPSy?

<http://www.gpsy.com/>

Although none of us on staff have a good reason to use a GPS unit in the near future, we were tantalized by three factors: the futuristic ability to pinpoint one's position on Earth using orbiting satellites, the fact that Karen offered to write an article about a subject that interested us, and the chance to play with cool toys.

Preparing to Race Satellites -- Karen shipped us a copy of GPSy and DeLorme's Street Atlas 3.0, along with two GPS units, a Garmin GPS 12XL and a DeLorme TripMate. I can picture taking the Garmin on a mountain expedition, with its small backlit LCD display and lots of control buttons. The TripMate, on the other hand, was just a waterproof yellow pod - no controls, no screen, just a black cable snaking out of one end.

<http://www.delorme.com/StreetAtlasUSA/>

In order to use GPSy in conjunction with Street Atlas, I needed a CD-ROM drive, so I borrowed a friend's PowerBook 3400c (which has an internal CD-ROM drive). Because I only had the GPS units for a couple of days, I drove to Adam and Tonya's house to try everything out.

Setting up the software was simple. The fat binary version of GPSy 2.1 is only about 850K, and installation was a matter of dragging the software from a floppy disk to the PowerBook's hard disk. (The current version, GPSy 2.5.3, was in beta when we tested the product.) Installing Street Atlas was also easy.

Our first troubles involved the hardware. Believing that any consumer device should be operated without reading the full documentation, we attempted to configure the Garmin unit. After a period of fiddling and pushing buttons, however, we resorted to the manual. The fact that it was cloudy and rainy outside also made it difficult to lock on to more than two or three satellites at a time.

Eventually we scrapped the Garmin in favor of the TripMate, which hadn't been misconfigured by human hands, and which, in this case, was easier to hook up and send data to the PowerBook.

A World of Data -- The information that the GPS units receive can seem like a fire hose of bits and bytes, and GPSy offers plenty of variations for displaying it. Clearly, GPSy is geared for the gear-head - or at least someone familiar with the many acronyms and terms associated with the field of global positioning. Here's an example of the raw information we received from the satellites (the NMEA Data field scrolls constantly):

NMEA Device: GP - Global Positioning System (GPS)
NMEA Sentences: [ APB BWC DBT GGA GLL GSA GSV MTW VTG ]
NMEA Data:
 $GPAPB,A,A,0.0,R,N,V,V,13.6,M,001,14.0,M,16.8,M
 $GPGGA,215043.54,4123.46,N,07254.86,W,1,04,2.0,00086,M,,,,
 $GPVTG,357.2,T,10.9,M,21.7,N,40.2,K

Even with this barrage of data, we had no difficulty figuring out how to use GPSy's main features, even if the terminology swept past us. Multiple windows for translating data can be accessed both via the Displays menu and numbered keyboard shortcuts. Command-1, for example, brings up a small window with the unit's precise location (taking into consideration the government-mandated "selective availability").

We found windows for heading, navigation (bearing), maritime and aviation data, and (my favorite) a visual representation of the satellites currently being tracked above, color-coded according to the strength of the signal. You can also bring up a world map with your location, although a pixel on that scale could represent several towns or counties.

In addition to displaying the data, we played with options for transferring commands and data to and from the GPS unit, such as routes and waypoints. GPSy also has the capability to speak the location and other information, using Apple's PlainTalk technology.

<http://speech.apple.com/>

On the (Sometimes Nonexistent) Road Again -- After playing with GPSy, it was time to throw a real-world test at it (and time for me to drive home). We launched Street Atlas and easily determined our position by choosing Locate Once from the GPSyLink menu.

Although Karen suggested that the TripMate unit would work best if duct-taped to the top of my car, I opted to preserve the paint and set the unit on my dashboard. Making sure that everything was running smoothly, I started GPSy's logging feature, and set off for home.

I was surprised to discover that the software kept up with me, with a lag of only a second or two, even though the night was rainy. GPSy displayed my heading and location, and registered how many miles per hour I was driving (a possibly useful feature if you're ever pulled over for speeding and want to prove your innocence, although the officer might be dubious about how well you're paying attention to the road with such a neat gizmo next to you).

In the Street Atlas window, a tiny blue car followed roughly the same path that I drove. Again, due to the "selective availability" limitation of consumer GPS devices, the little icon wasn't always right; I would occasionally see the car burrowing through a thatch of trees or skimming over a nearby lake. Still, it was refreshing to see such a quick response to data beamed in from above.

Lost Highways -- Using GPSy and the GPS units convinced me that the idea of embedding GPS receivers into cars and other vehicles isn't so much a pie in the sky idea as I had assumed. That's good news for me, because despite the help of satellites and a constantly updating map, I still took a wrong turn trying to get home.

GPSy costs $30 shareware and requires at least a 68020-based Mac running System 7.0 or later. A demo version, which is limited to 15 minutes of use per launch, is available as a 750K download.

<http://www.gpsy.com/download.html>

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GPSy 3.0 Maps New Features -- Directionally impaired Mac users will be relieved to learn of the release of GPSy 3.0, Karen Nakamura's software for working with data from Global Positioning System (GPS) satellitesShow full article

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GPSy 3.0 Maps New Features -- Directionally impaired Mac users will be relieved to learn of the release of GPSy 3.0, Karen Nakamura's software for working with data from Global Positioning System (GPS) satellites. With a GPS receiver, a Macintosh, and GPSy, you can pinpoint your location to within 100 meters anywhere on Earth (the GPS system is capable of tracking to one sixteenth of an inch, but that capability is reserved for use by the U.S. military; see Karen's article "Feeling Lost? An Overview of Global Positioning Systems," and a review, "Driving Through Trees: Using GPSy," in TidBITS-388). In addition to protocol additions for working with a wide variety of GPS units, GPSy 3.0 adds the capability to view your position using information from several Internet map servers, such as the U.S. Census TIGER Mapping Service and Geocities. GPSy is $50 and available as a 1 MB download. [JLC]

<http://db.tidbits.com/article/02222>
<http://db.tidbits.com/article/02223>
<ftp://ftp.gpsy.com/pub/software/ GPSy300.sea.hqx>

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Sitting at a glowing screen for hours on end, with little or no live human interaction - this is the typical Internet experience. But some areas of the Internet compel users to leave the keyboard, go outside, and interact with the real worldShow full article

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Sitting at a glowing screen for hours on end, with little or no live human interaction - this is the typical Internet experience. But some areas of the Internet compel users to leave the keyboard, go outside, and interact with the real world. This category of Web sites, hugely popular and usually non-commercial, doesn't have a name yet. Because these sites promote an activity or hobby - even a lifestyle - beyond the Web, they're more of an online/offline phenomena. I've dubbed the aggregate of these Web sites "Internet-Guided Offline Recreation" (IGOR). IGOR is different from sites that merely discuss offline recreation, like sailing or knitting, because the activities are mediated and tracked by - and essentially inseparable from - their Web sites.

GPS Games -- On 01-May-00, the Clinton Administration ended the U.S. government's policy of Selective Availability, the intentional degradation of Global Positioning System (GPS) signals. The new availability of GPS to the civilian population had practical applications for telecommunications, emergency response, transportation, and industry. It also launched a new form of recreation.

<http://www.ngs.noaa.gov/FGCS/info/sans_SA/docs/ statement.html>

Only two days after the end of Selective Availability, someone hid a logbook inside a container near Portland, OR and posted its GPS coordinates on the sci.geo.satellite-nav newsgroup. Just three days later, the container, called a "cache," was visited twice, the visits recorded in the logbook and online. From the immense curiosity, immediacy, and coolness factor that this generated, a high-tech hide-and-seek game was born: geocaching.

<http://www.geocaching.com/about/credits.asp>
<news:sci.geo.satellite-nav>

Geocaching.com, the first and most trafficked Web site devoted to geocaching, facilitates seeking and creating new caches. The caches are registered in the Geocaching.com database according to "waypoints," short names representing the identifications of specific caches. Each waypoint is associated with GPS coordinates that indicate the exact location of the cache.

<http://www.geocaching.com/>
<http://www.trimble.com/gps/>
<http://www.pbs.org/wgbh/nova/longitude/gps.html>
<http://www.groundspeak.com/>

The Geocaching.com site enables searches for any relevant data: zip code (within a user-defined radius), location, coordinates, keyword, area code, waypoint, or geocacher's username. For example, if you search for waypoint GC78A5, you'll find a geocache called "Stock Market CrACHE in Twin Peaks." The details page provides the coordinates, difficulty and terrain ratings, notes and encrypted clues (easily decrypted by the "cheater" link), zoomable map, and log entries and photos from other geocachers.

<http://www.geocaching.com/seek/cache_ details.aspx?ID=30885>

Most caches are hidden in parks, wilderness areas, and other public spaces. When hunting for a cache, it helps to have both GPS coordinates and clues in hand - but also look for the telltale path of trampled grass that often betrays the hiding place.

Some caches are so challenging that finding them might require more than one attempt. The coordinates are accurate to about 15 feet (4.6 m) at best - which, when multiplied by two (to account for the margin of error of both GPS units, the hider's and your own) is 30 feet (9.1 m) - and beyond that, you're on your own. I had to return to "Sounds of the Bay" after my first unsuccessful search because the cache could have been hidden in any of the myriad crevices of the loose-rock wharf, and even the "spoiler" photograph of the geocache owner pointing to the hiding spot didn't help.

<http://www.geocaching.com/seek/cache_ details.aspx?ID=12491>

A "Traditional Geocache" (marked by a generic icon) is an airtight, waterproof container that stores a logbook and pen for on-site comments, a disposable camera, and some goodies. The idea is for geocachers to sift through the goodies, take one, and add something new. Don't expect to find a wad of cash or valuable jewelry in a geocache; prizes usually comprise old toys, coins, seashells, and trade convention gewgaws. But getting stuff isn't the point of geocaching; the real prize is just finding the cache and admiring the view while you're there.

Another type of geocache is a "Multi-Cache," which contains a clue in the first cache that leads the geocacher to a second cache and possibly more after that. Sometimes these can be all-day affairs, involving clues, puzzles, or riddles, for which only hard-core geocachers have the necessary time and patience. (The Geocaching.com Web site, previously all non-commercial, recently launched a premium service for such serious geocaching.)

Sometimes you won't get a prize at all - at least not one you can take with you. A "Virtual Cache" has no hidden container: the location itself is the prize. (The details page may ask you to answer a specific question about the location or to perform a task.) An "Event Cache" involves both space and time; geocachers go to a certain location at a certain time to meet other geocachers. Avid geocachers frequently check the Events Calendar to see when an Event Cache is happening in their area.

<http://www.geocaching.com/about/cache_types.asp>
<http://www.geocaching.com/about/calendar.asp>

Seek and Hide -- Of course, you're not limited to just seeking - you can create your own cache as well. I recommend finding at least one geocache before establishing your own to learn what works well and what the best caches offer. You're responsible for the caches you hide, which means visiting them occasionally, cleaning out debris, replacing cameras when film runs out, and adding new stuff. If you're lazy or don't have much time to visit your geocache, hide it close to your home to avoid traveling extensively to check it. And read the instructions carefully; I mistakenly hid a cache in Land's End, which is part of the Golden Gate National Recreation Area and therefore federal land - a geocaching no-no. Since it's across town, I have yet to retrieve it. Further, use good judgment based on your knowledge of the area. I hid a geocache containing a beautiful handmade logbook and a bag of candy in what I thought was the perfect hiding place: the trunk of a large evergreen tree. But, because the tree is in San Francisco, a homeless person moved in underneath the branches, and my cache not-so-mysteriously disappeared.

I started with three hidden geocaches, and now have only one left, but I am quite happy with it. It's in a beautiful, easily accessible area, so it's visited often. I developed the film of its first disposable camera onto prints and a photo CD, whose images I uploaded to the geocache details page. Before I looked at the prints, I hadn't quite realized what a marvelous hobby geocaching is. No two photographs were alike. In several pictures, a man stood alone, sometimes staring off-center because he's taking his own picture. Other pictures showed couples and groups of friends, smiling or sticking out tongues. A young father posed with a baby in a backpack carrier, a dog shivered in the wind, a too-close wristwatch blurrily displayed the time, and a toy lay on the grass. Photos were taken from different directions and perspectives, at different times of day (including one wigged-out guy at night), during different seasons, and in different types of weather (sometimes clear and sunny; other days, foggy). I slid the prints into a cheap pocket-sized photo album, labeled it "See the geocachers who have come before you!", and added it to the cache.

Spin-offs -- A testament to the popularity of Geocaching.com is its spin-off sites. Navicache.com offers the same thing as Geocaching.com, but with a more amateurish site and fewer registered caches. Geocaching Worldwide began specifically for Australians and later expanded to include caches located around the globe. Geodashing turns geocache hunting into a race to find one cache after another (uploading photos as proof), and has appropriately renamed "waypoints" as "dashpoints." Befitting the patriotic times, CacheAcrossAmerica has successfully established a chain-link of geocaches across the continent, following the approximate path of Interstate 80. The burgeoning EcoScavenger encourages geocachers to "share places rather than stuff" - a nice idea but already covered by Geocaching.com's virtual caches. Inspired by the cheap plastic toys in Hasbro's classic Barrel of Monkeys, a couple of jokers created a very serious Web site that invites geocachers to Linn Run State Park in Pennsylvania to conduct "monkey research."

<http://www.navicache.com/>
<http://www.geocachingworldwide.com/>
<http://geodashing.home.attbi.com/>
<http://groups.yahoo.com/group/ CacheAcrossAmerica/>
<http://www.ecoscavenger.com/>
<http://www.monkeycache.com/>
<http://www.geocaching.com/seek/cache_ details.asp?ID=2716>
<http://www.hasbro.com/games/pl/page.viewproduct /product_id.8616/dn/>

Geocaching aficionados appreciate Buxley's Geocaching Waypoint, a companion guide chock-full of interesting stuff. Buxley's world map of cache sites reveals the predictable pattern of a hobby for the techno-elite (that's us): the vast majority of caches are hidden in the United States (and southern Canada) and Western Europe; the rest are hidden in coastal areas of Australia, Central and South America, South Africa, major Asian cities, and Pacific islands. In other words, even though geocaching is a relatively inexpensive hobby, players live in and travel to "rich" areas and so obviously have enough food, shelter, and disposable income to afford GPS units and Internet-connected computers. Buxley's also keeps a log of geocaching news and unique caches that involve more than waypoints and containers.

<http://www.brillig.com/geocaching/>

Getting Started with Geocaching -- One of the major draws of geocaching is that it's a relatively inexpensive and easy hobby to participate in. A bare-bones handheld GPS unit, which you can buy for about $100, can read satellite signals and triangulate fairly accurate coordinates - all you need to get started on your first geocache. For around $350, a fancy GPS unit includes features like downloadable mapping, waypoint storage, an altimeter, and other geeky but useful stuff. Other units work specifically in cars, and some combine GPS capability with fish-finders and water-navigation tools.

<http://gpsinformation.net/>

GPS games are an innovative way to combine computer nerdism with outdoor adventuring. It costs next to nothing and inspires eager novices to join the "secret society" of geocachers. It's easy to get addicted (some geocachers seek hundreds of caches per year), but as vices go, this one's not so bad.

In the next installment of this article, I'll explore a few other variations of geocaching, such as tracking currency around the world, exchanging physical notebooks, and more. See you at the next waypoint!

[Mariva H. Aviram, author of several books and numerous articles, has a passion for the outdoors, art, books, film, culture, and satire. More information can be found at her Web site.]

<http://www.mariva.com/>

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Have you ever found yourself driving at high speed or in heavy traffic in an unfamiliar area while the person in the passenger seat frantically attempts to read the map and tell you where to turn next? If you're like me, it's stressfulShow full article

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Have you ever found yourself driving at high speed or in heavy traffic in an unfamiliar area while the person in the passenger seat frantically attempts to read the map and tell you where to turn next? If you're like me, it's stressful. And if you're anything like Tonya, trying to figure out the current location on a map and give coherent directions, all while the car is moving is equally as stressful, plus a bit nausea-inducing.

Our recent trip to New Mexico was made even more enjoyable by our decision to spring for the extra $10 per day to rent a GPS-enabled (global positioning system) cell phone from Alamo that spoke directions for each upcoming turn. It was brilliant, despite some notable design flaws. We're not gadget freaks, but we've already decided to look into buying a similar device for the next time we have to do any significant driving in unknown parts.

Driving by Wireless -- Alamo wasn't forthcoming about what the device actually was and how it worked, so my apologies in advance if my deduction and speculation prove somewhat incorrect. From what I could tell, the GPS device itself was a Motorola i58sr cell phone with Nextel service; the phone had a relatively small black & white screen, and Alamo provided a suction cup mount so it could attach to the windshield.

When turned on, the phone ran some kind of specialized Java application that asked for your permission (presumably because you could have been tracked through the device) and then dumped you into a predictably lousy interface for searching for an attraction or entering an address. Once you entered the address, the phone used Nextel's data network to download driving directions from your current location, determined by the GPS, and then both read them out loud to you via its speakerphone and displayed the next turn on the screen, with running countdowns of how far until your next turn and until you reached the eventual destination. It always started talking about half a mile away, and it repeated itself as you got closer, but never so much that it was annoying. As you came up on a turn, a progress bar showed you how many meters until the turn; that was great in situations where there were two turns quite close together.

Although the interface was poor, and it took us longer to figure out than ideal (remember, we were driving; it's not like you have time to sit down with the thing beforehand, and Alamo didn't include any instructions at all), we quickly became addicted to the driving instructions. With one exception - where the GPS phone would have had us get off an arterial, cross a road, and get right back on - the instructions were extremely accurate. And interestingly, a second pass through the area where it gave the foolish instructions did not repeat them; it's conceivable that we were in a different lane and thus triggered different instructions. If you missed a turn (the mistake was the only direction we ignored), it detects that you're not on course and quickly downloads new directions to reroute you.

More problematic, particularly in the rural parts of New Mexico, was that you had to enter a full address. We were staying with fellow authors Robin Williams and John Tollett for a few nights, and although we had directions to their house, and thus had the final road name, we didn't have their street address handy. We were able to fool the GPS phone into giving us directions anyway by guessing that the house number was 1 instead of 2745 or something, and we were lucky, since in some cities, that difference could have put us entirely across town. A bed and breakfast we stayed at in Chimayo had only a P.O. box for an address, and the device's database had never heard of County Road 0100, so it wasn't much help there.

Although Tonya found a GPS menu in the phone's interface somewhere, we never managed to see if it would give us a map view of the area (and my reading of the phone's user's guide afterwards would seem to indicate not). It would have been helpful to be able to point at a spot in the map and say "Go there!" It would also have been useful on at least one occasion to see a map view and which direction we were traveling; luckily my normal handheld GPS device showed us that we were headed in entirely the wrong direction. That was before we'd quite realized how helpful the GPS phone would be, and we hadn't planned on using it that trip, since our final destination in Los Alamos didn't have an address (it was probably classified information, though we were again able to fool the phone into taking a random address on the final street). According to the user's guide, the phone can communicate with a computer to work with mapping software, though it was unclear if it would really work on the Mac or not.

<http://nextelonline.nextel.com/assets/pdfs/en/ support/guides/phones/i58sr/ug.pdf>

As you might expect, the reliance on Nextel's data network for instructions proved problematic in several locations, since Nextel's coverage where we were in Taos and Santa Fe was poor to non-existent. We were fine getting to those locations, since the phone downloaded all the instructions it needed initially, but it couldn't access any new instructions until we were within range of a Nextel tower again.

Planning for the Next Trip -- Such voice-enabled GPS devices are not new; I've been hearing people talk about them for years. But they're pricey ($400 to $1,000), and particularly in Ithaca, where we know the roads well, I couldn't justify the expense of such a device. But this GPS phone and associated service, thoroughly mediocre though it may have been, fell squarely into the category of gadgets that improved our life. Particularly when I'm under time pressure to arrive somewhere, I'm not one of those people who is relaxed about potentially getting lost. I hate not knowing where I am, and I absolutely can't stand the feeling that I'm going to be late because I took a wrong turn somewhere. And in turn, Tonya doesn't enjoy reading maps and feeding me navigation instructions while we're driving. So the clearly enunciated directions both increased my peace of mind while driving and Tonya's relaxation level.

I've started to look into other devices that might work better than the Motorola GPS phone; it's not acceptable to be without directions just because you can't get cell service. It also sounds from this PC World article as though it would be fairly expensive: the cost of a Nextel data plan plus $11 per month for the GPS service.

<http://www.pcworld.com/reviews/article/ 0,aid,115273,00.asp>

There are a number of dedicated GPS devices that promise features well beyond what the GPS phone provided, such as multiple map views, route choices if you don't want to take freeways (or if you want to take only freeways), and more. Voice instructions are key, since paying attention to gadget interfaces in the car is dangerous. A few of the devices I've found and plan to look into further include:

• Magellan RoadMate 300/500/700
  <http://www.magellangps.com/en/gpsAdventures/ driving/road.asp>

• Garmin StreetPilot c320/c330/2610/2620
  <http://www.garmin.com/mobile/ products.html#automotive>

• TomTom GO 300/700/Rider
  <http://www.tomtom.com/products/category.php? ID=0&Language=4>

If you've used one of these devices, or another voice-enabled GPS system for providing navigation, let us know on TidBITS Talk <tidbits-talk@tidbits.com> what you think.

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It's 11:00 PM, and we're in moderately heavy traffic on the Tappan Zee Bridge on our way into New York City. Our directions, passed down in the family for generations (well, at least it seems that way) say to take the second exit after the bridgeShow full article

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It's 11:00 PM, and we're in moderately heavy traffic on the Tappan Zee Bridge on our way into New York City. Our directions, passed down in the family for generations (well, at least it seems that way) say to take the second exit after the bridge. Counting down, it's exit 9, then exit 8A, then exit 8... clearly we should take exit 8A, except that 8A is for I-87, whereas we're supposed to be getting on the wonderfully named Sprain Brook Parkway next. Traffic's moving too quickly, and I've already committed to exiting by the time Tonya has realized that we really should have taken exit 8.

<http://www.nycroads.com/roads/sprain-brook/>

Under normal circumstances, this mistake would have been cause for much gnashing of teeth, rending of hair, and unkind words directed, at the least, at the transportation engineers who designed the confusing interchange. But these aren't normal circumstances, and we're driving with the aid of a Garmin StreetPilot c330 GPS device that is calmly, without allowing even the barest hint of peevishness in its voice, giving us directions that will take us to the Throgs Neck Bridge via the Hutchinson River Parkway. At 11:00 PM at night. In the dark. On roads we've never before seen. And it does so with complete success, directing us to the hotel in Queens where my family has gathered to attend my grandfather's funeral the next day.

The funeral was unanticipated, though due the medical care being committed upon my grandfather, not entirely surprising. Nonetheless, we had only 24 hours notice, a TidBITS issue to edit, a DealBITS drawing to coordinate, several deadlines related to our Take Control of Tiger collection for Peachpit, and the usual packing and trip preparation. Luckily, I was able to lay my hands on the StreetPilot c330 to test in the real-world mean streets (and freeways and expressways and parkways and turnpikes) of New York City. New York may not be the ultimate test of a GPS, but it certainly ranks up there in terms of complex and stressful driving.

<http://www.garmin.com/products/sp330/>

Last week, when I wrote about using the Motorola i58sr GPS-enabled cell phone, I noted that I was disappointed in its reliance on having a clear cell signal to download instructions, the lousy interface for entering destinations, and more. The StreetPilot c330 addressed all those issues and fared poorly in only some comparisons. And well it should, given that its suggested retail price is $964.27.

<http://db.tidbits.com/article/08111>

In the Flesh -- Physically, the StreetPilot c330 is well-designed, and far more so than the GPS-enabled cell phone. Rather than the candy bar shape of the cell phone, which forces the screen to be relatively small to make room for the keys, the StreetPilot c330 is nothing but screen. It ends up looking similar to a dehydrated original iMac - slightly lozenge-like. Its 3.5-inch (8.9 cm) backlit screen offers 320 by 240 resolution with 16-bit color; almost all functions are accessible via the touch screen, eliminating the need for a keypad of any sort. It features an integrated lithium battery with a reputed 4-hour battery life; our trips to and from New York City were in the 3.5 hour range, and we had no problems with the battery conking out. The only physical controls are a rotary volume knob and an on/off switch. It fits snugly into a decently designed suction cup mount that attaches firmly to the windshield.

The screen was clear and easy to read, except in bright sun, and wearing sunglasses to combat the bright sun made the screen only harder to read (that was one area where the monochrome screen of the GPS-enabled cell phone succeeded). At dusk, the StreetPilot c330 automatically changed the display colors from a yellow background to a black background to reduce the distraction of a bright light in the driver's field of vision. The touch screen itself worked flawlessly, and the device proved trivial to use without reading any directions at all.

Having a battery, which isn't standard across competing devices, proved to be particularly helpful, since that meant we could use the StreetPilot c330 while leaving our iPod in the DLO TransPod plugged into the single outlet in our Honda Civic. We dislike the TransPod and will replace it at some point, but for now, it's a functional solution to the problem of how to listen to the iPod in the car with a minimum of cabling snaking around the cabin. If we needed to plug two units into the same outlet, there are apparently adapters that provide a pair of outlets from one. Unfortunately, the StreetPilot c330's plug was integrated into the suction cup mount, so it was impossible to avoid its dangling cable even when we were running from battery power. The StreetPilot c330 also comes with an AC adapter that charges the battery from a normal wall outlet.

All in Its Head -- One key reason for testing the StreetPilot c330 for this trip was that it had all its maps pre-loaded, eliminating the need to figure out how to load maps from a PC via USB. I have an old Garmin eTrex Legend handheld GPS, and loading maps into it requires a PC with a serial cable (a USB adapter might work, but since I have an old PC that does nothing but load maps into the GPS, I haven't looked into making it work on my newer PC). Although I'm confident that I could have done the map loading, I dislike being forced to use a PC, and the software is neither Mac-compatible nor will it work (reportedly) with Virtual PC. More to the point, I didn't have the time or energy to load maps before this trip. Also loaded automatically was a database of points-of-interest; we had no opportunity to use it since the trip was so focused. One downside of the StreetPilot c330 (and all devices from Garmin, I believe) is that it comes with only a single free update; after that database upgrades cost an extra $150 (prices vary with other parts of the world), which feels excessive after buying a nearly $1,000 device.

Using the StreetPilot c330's interface is simple and elegant. Upon powering up, it displays two buttons: Where To? and View Map. Clicking Where To? walks you through the process of entering an address: state, city, street number, and street name. At each point, the StreetPilot c330 provides a list from which to choose as soon as it has seen enough characters to narrow the choices. For instance, I had to enter only IT before it guessed "Ithaca" properly, although, oddly, it wouldn't accept two-letter state abbreviations. Annoyingly, and I gather that this is true of other GPS devices as well, it was persnickety about the city. In New York City, different areas have different city names, so even though we were in Queens, in New York City, we had to know that the hotel was actually in the city of Bayside and my grandparents' old house (where Tonya and Tristan and my sister and I all visited when we had some free time) was in actually in Fresh Meadows, even though we'd always written Jamaica for the city in their address. When possible, the StreetPilot c330 remembered the current state and city so all I had to do was click the New York button instead of entering New York as the state each time.

Although the StreetPilot c330 has only a single female voice, it was clear and easily understood at all times, though we did have to max out the volume in most freeway and city driving. Occasionally, on smaller streets, I lowered the volume a notch for aural comfort. I didn't particularly need a choice of voices (I gather that people with the beginnings of hearing loss appreciate a choice), but the main thing I found disappointing about the StreetPilot c330 was that it has only a small vocabulary that covers the words necessary to say how to turn, what direction to turn, and how far away the turn is. The GPS-enabled phone also spoke the name of the road we were turning onto, which was great, since it eliminated the need to look at the screen at all. Since the StreetPilot c330 lacked that feature, I found myself constantly glancing at the screen to see the name of the next turn, and although I'd positioned it well for that use, anything that distracts from looking at the road can be dangerous.

That said, I found looking at the 3-D map display particularly helpful in two situations. First, when we were driving quickly on Route 17 toward New York City at night, there were sometimes major curves in the road that I couldn't anticipate in the dark. But seeing them represented a few hundred meters ahead on the StreetPilot c330's screen enabled me to tell what was coming up. Similarly, when exiting from freeways, being able to see what squirrelly off-ramps looked like ahead of time was extremely welcome.

The StreetPilot c330 has a decent set of options, although I gather that other devices may offer more. For instance, the slightly more expensive Garmin StreetPilot 2620 can accept a series of destinations in a route and can theoretically route around temporary problems such as traffic jams or roadwork (not automatically, the user must specify roads to avoid, though we would have been happy to do that while we were caught in terrible traffic on the Cross-Bronx Expressway on the way home). It also lets the user choose whether it should prefer large, medium, or small roads and includes a remote so a passenger can interact with it without leaning forward all the time. But on the downside, it can't run from battery and looks more complex to use.

<http://www.garmin.com/products/sp2620/>

You Get What You Pay For -- I can't say for sure if the StreetPilot c330 will prove to be the GPS navigation device we end up with. Aside from the difficulty of reading the screen in direct sunlight and its inability to read the names of turns out loud, we liked it a lot, and if it were the only option, we'd be happy with it. But at discount prices starting around $750 and with the promise of one or more $150 database upgrades in the distant future, it's not cheap, and we don't do that much driving in unfamiliar areas. Of course, we'd probably rationalize some of the cost by lending it to family and friends on occasions when we didn't need it, but still... And now that we've been bitten by the GPS navigation bug, additional research into competing units from Garmin, along with Magellan and TomTom, is clearly in order. For more anecdotal reviews of other GPS devices, be sure to read the TidBITS Talk thread that's collecting excellent comments from other TidBITS readers.

<http://emperor.tidbits.com/TidBITS/Talk/456/>

In thinking about how to reduce the cost, I also researched the Garmin StreetPilot c320, which differs only in that it comes with a 128 MB SD card for holding maps, which must be loaded from a PC. It reportedly accepts SD cards up to 1 GB for holding lots of maps, which would add about $75, but since the StreetPilot c320 costs only slightly less than $700 at discount, there wouldn't be any particular savings over the pre-loaded c330.

<http://www.garmin.com/products/sp320/>

Oh, remember the problem with our family directions? It turns out that exit 8A is relatively recent, and when the directions were written, it didn't exist. Change happens, but it won't cost anything to get new directions from my mother.

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I have been running regularly for many years. Although I gave up competing 20 years ago, I still like to jog around the lanes and footpaths in Cornwall, England for an hour or so each morningShow full article

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I have been running regularly for many years. Although I gave up competing 20 years ago, I still like to jog around the lanes and footpaths in Cornwall, England for an hour or so each morning. Until recently the limit of my record keeping and analysis was to file the number of minutes for each run, to make sure I maintained a reasonable average month-by-month. These days I am more interested in the views than in how fast I might be going.

All that changed three months ago, when on an uncharacteristic impulse I bought a Garmin Forerunner. It is a little device that you wear on your wrist like a bloated watch. It uses the Global Positioning System (GPS) to measure how far you travel as well as the time you take, and thus allows you to record far more information about each run than you could manage with a normal stopwatch.

<http://www.garmin.com/outdoor/ products.html#fitness>

What Is the GPS? Although previous TidBITS articles have explained GPS in more detail (see the series "Find Yourself with GPS"), a brief refresher might be welcome. (For a full explanation of the system, see Karen Nakamura's "Feeling Lost? An Overview of Global Positioning Systems" in TidBITS-388; it was written before the accuracy of the GPS system was "improved" for civilian use, but is otherwise helpful.) The GPS relies on signals from a network of 24 satellites that orbit the earth at altitudes of between 6,000 and 12,000 miles (roughly 10,000 to 19,000 km). A GPS device like my Forerunner needs signals from at least three satellites to fix its position in two dimensions, and from four to estimate its elevation above sea level. It updates its position more or less constantly and can therefore track the distance, direction, and speed of movement.

<http://db.tidbits.com/series/1264>
<http://db.tidbits.com/article/02222>

In the early years of the GPS, the U.S. Department of Defense imposed "Selective Availability" (SA) to degrade the accuracy of the system for non-U.S. military purposes, so civilian devices were accurate to about 100 meters. However in May 2000 SA was turned off, and since then the system is typically accurate to within 15 meters, according to Garmin.

Real world accuracy varies around this figure. The more satellites the device can detect, and the more widely spaced they are, the more accurate is the reading. In the U.S. the Wide Area Augmentation System (WAAS) can improve accuracy to less than three meters for WAAS-enabled devices like Garmin's StreetPilots (but not the Forerunner series). However, tall buildings, dense foliage, changes of direction, and other nuisances can interrupt signals or restrict the number of satellites the device can detect, as we will see, so 15 meters is only a guide to the accuracy you can expect.

<http://www.garmin.com/aboutGPS/waas.html>

What the Forerunner Can Do -- The Forerunner enables you to divide your run into as many "laps" as you want, and record the time, distance, average pace and numbers of calories burnt for each lap. You can define the laps either automatically according to a set distance, say one mile or one kilometer. Or you can press the Lap button as you pass turnings or other landmarks along the way. Regardless of the numbers of laps, the Forerunner keeps track of the total distance covered, total elapsed time, overall average pace and the best pace you achieved during the run. You can also have it record the amount of "rest" you take, which is defined as moving slower than a certain pace that you specify.

You can set up targets for your run by setting a pace for your "virtual training partner" and having the Forerunner keep track of how far ahead or behind you are. Or you can define a set of intervals where you alternately run fast, jog for a while to recover and then speed up again, one of the most effective (and exhausting) ways for competitive athletes to improve their performance.

The Forerunner has three main 64 by 100 pixel data screens, and each screen can show three pieces of information. The first, Timer, screen shows the elapsed time, current pace (minutes per mile or kilometer) and total distance for the run. The second screen shows the same information for the current lap, and the third you can customize, so you might choose, say, time of day, best pace achieved so far, and elevation.

The history mode records all the above information for your last run and summarized by day and by week. Garmin says the Forerunner can store information from 5,000 laps.

The Forerunner can map your track and show it as a dotted line on its screen, either for the whole run or for each lap, punctuated with any location points that you choose to define. It is not capable of receiving and displaying uploaded map information, so you cannot follow your progress along roads in the way you can with a car navigation system like a StreetPilot. But it does have a TracBack mode to help you find your way back to the start or some other known point in case you get lost.

How It Actually Performs -- The Forerunner weighs just 2.75 ounces (78 grams) which is nearly unnoticeable on your wrist; it is easy to set up and use; the data screens are easy to read while running; it does all you would expect and that the manual claims; and it certainly adds something to your running experience. It is good to know how fast you are going, however unforgiving the minutes may often be. But the Forerunner has a few quirks that have made me curious about exactly what is going on inside and how accurate it is.

I have compared different measures of distance between the same physical points, taking care to follow the same track each time. The same run, repeated exactly on two days, showed up as 6.73 and 6.90 miles, a difference of about 2.5 percent. For six measures of a roughly 1.5 mile circuit, the range from highest to lowest result was 0.05 miles (264 feet), or about 3 percent of the average of the six measures. This level of accuracy seems typical where I have a relatively open view of the sky most of the time and no more than a fifth of the route is narrow with overhanging branches.

I occasionally hear the plaintive beep that the Forerunner lets out when the GPS signal is weak, and that is where the distance readings become the least consistent. For four measures of a section of about 0.7 miles where the lanes are lined with high, solid hedges and often overhung by trees, the range was a whopping 22 percent.

For what I thought would be a definitive accuracy test I took my Forerunner to a local 400 meter track, located on a piece of land that is flat and open by local standards, with no tall buildings and few trees near enough to affect the readings. To my surprise, the level of accuracy was less good than in my earlier tests, ranging from 383 to 425 meters over four laps, which was between 4 and 6 percent off.

When I asked Garmin about this result they said a good satellite "fix" at the start is critical for such tests, especially when running a circuit where the device must update its position from different satellites as you change direction, and in this case I might not have given the Forerunner enough time to get a good initial view of several satellites. In their own tests they used a wheel to measure a local running track at 398 meters, and for 14 laps the Forerunner recorded from 393 to 402 meters, with an average error of 0.56 percent.

The current pace on the main screen is one of the readings I like to look at. It is usually plausible but occasionally changes dramatically within a short distance for no obvious reason, not necessarily where the sky is most obscured. And I am curious about the distance over which the Forerunner calculates the best pace of the run, which sometimes seems a bit too good to be true. Garmin was coy about the frequency of calculation and other details of these numbers.

When I stand in front of my house looking south at almost 180 degrees of open sky and sea, the elevation reading changes by a foot or so every second, over a vertical range of anything up to 30 feet. Even though the Forerunner knows about elevation, Garmin acknowledges that it is more difficult to pin down than location, and the Forerunner does not include elevation in its calculations unless the readings are stable enough to be reliable. On one run it showed I had burned 40 calories on a lap that I marked while struggling painfully up the steep hill from my house, but 75 calories when running the same lap more quickly but far more easily on the way down at the end.

Alternatives -- Garmin makes three Forerunner models. The 101 (about $100 street price) runs off two AAA batteries and does not allow you to transfer your data to a PC. My 201 (about $140) runs off a rechargeable battery that holds a charge for 15 hours of use and allows transfers, using Training Center software that Garmin makes available on its Web site; Training Center enables a PC (but not your Mac, sadly) to track your runs on street maps and carry out more sophisticated analyses of your past runs. The main feature of the newest member of the Forerunner family, the 301 ($250), is that it uses a chest strap-mounted sensor to record your pulse rate in addition to time and distance. It also comes with a CD that contains a more sophisticated version of Training Center that enables you to plot your pulse rate at any point along the way, and plan future training sessions based on an assessment of your performance so far.

Overview -- I am pleased with my Garmin Forerunner mainly because it adds a new level of interest to my runs. Call it a new level of challenge if you are that way inclined. Even at my sedate pace it has probably made me run a little faster, and I can vary my pace more systematically, so perhaps I am in slightly better shape than I was three months ago. I can live with the level of accuracy that the Forerunner can manage in my testing environment of Cornwall. I certainly prefer it to other distance-measuring devices that depend on maintaining a constant stride length, which aside from being difficult goes against the principles of fitness training that I learned in the dim and distant past.

As a Mac user I would like Garmin to put out versions of its software that I could actually use, although Garmin says they have no plans to do so, and in practice I am not sure I would use it much because the Forerunner already displays enough information for my needs. It does not take much effort to type one or two key figures into a spreadsheet each morning. If you are keen enough you can get software from other sources, such as Hiketech (for the Mac) and Motionbased (for Windows, with Mac support promised), which enables you to upload and map your runs.

<http://www.hiketech.com/>
<http://www.motionbased.com/>

For me, the Forerunner's main weakness is its inability to incorporate elevation into its calculations and analyses. Slogging up my Cornish hills can be hard work and I feel a bit cheated by not getting credit for all that effort.

[Paul Lightfoot is a freelance writer and consultant on international development projects. Now based in Cornwall, England, he has spent much of his adult life running around Asia.]

<http://homepage.mac.com/paullightfoot/>

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When I last wrote about GPS navigation, Tonya and I had just returned from the mean streets of New York City safely, thanks to the Garmin StreetPilot c330 GPS's voice-navigation instructionsShow full article

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When I last wrote about GPS navigation, Tonya and I had just returned from the mean streets of New York City safely, thanks to the Garmin StreetPilot c330 GPS's voice-navigation instructions. But perhaps the Garmin c330 wasn't the ultimate GPS navigation device. The other big name in GPS is Magellan, so I requested a review unit of the RoadMate 700, the model most comparable to the StreetPilot c330, thanks to its pre-loaded map set. The test? Our trip to Macworld Expo in Boston. Unlike New York City, it's easy to get to Boston from Ithaca; you just follow interstates to the Massachusetts Turnpike, which runs smack into the city. The problem is what happens once you get there, given that Boston is notorious for having some of the most, er... creative street layouts and markings. Would the RoadMate 700 take us successfully to and from our hotel, with some city street navigation through Cambridge on the way home?

<http://db.tidbits.com/article/08121>
<http://www.magellangps.com/en/products/ product.asp?PRODID=955>

The Hardware -- The RoadMate 700 is a bit larger and heavier than the StreetPilot c330 because the RoadMate