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Running with a Garmin Forerunner GPS

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.

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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.



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.


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.



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.]


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