Features | Data Fields
Distance, Time, Pace/Speed
The cornerstone of any GPS watch. This is the difference between a GPS watch and a standard sport watch. Briefly, distance is measured real-time, letting you know exactly how far you’ve gone. Time is, well, time.Pace is used running, usually in minutes per mile, and tells you how fast you are going. Speed is the same as pace, but it’s displayed as miles per hour, and is used in non-running activities (like biking). Every GPS watch can also display this information in both metric and imperial units.
These measurements can be displayed in real-time or in different lap permeations. Real-time is just what it sounds like: your current distance, pace (known as instant pace) or speed. Depending on the watch, lap stats can be displayed as last lap, lap average, fastest lap, slowest lap, etc.
One thing about instant pace: it’s a very difficult metric to accurately display. Running is a slow enough activity, and GPS is not accurate enough to display a steady pace. What tends to happen is that the instant pace jumps irregularly (think, 8:30 to 8:25 to 8:40 to 8:42 every second). And while watch manufacturers are getting better at pace smoothing, it’s still a work in progress.
A workaround is to ignore instant pace and display an average lap pace of, say, 0.25 miles. That lap distance is long enough to generate a more accurate pace (pace averages become more accurate over a longer distance), but short enough to notify you if you are above or below your desired pace. In fact, one watch, Garmin’s Forerunner 110, doesn’t even offer instant pace; it only has average lap pace.
Most often this is calculated using an algorithm based on basic personal information (namely, age, weight, and sex). This works ok for ballpark estimates but isn’t very precise.
Luckily, about half the watches available also offer heart rate calculated calories. This builds on the algorithm by including heart rate as part of the equation. This provides a better but still not perfect calorie count.
For the most accurate calorie measurements, a few Garmin watches can incorporate your profile after completing a VO2 Max test. This is highly accurate but involves going into a laboratory and doing a grueling treadmill test. Not for the casual athlete!
Not every watch displays elevation, but those that do use two different methods: GPS elevation and barometric elevation. Real-time GPS elevation – determined by satellite signal – is notoriously faulty. It will give you a rough estimate of your elevation, but like instant pace (only worse) bounces between different elevations with 100 foot variations. To compensate, many watches will smooth this data after you download it onto a computer.
Barometric elevation works by measuring atmospheric pressure. The catch is that a watch must be equipped with a barometer – not a common feature, it’s usually only found on costlier watches. And while this elevation data is much more precise than GPS, there are still flaws.
Cadence refers to how fast your legs turnover each stride (running) or while pedaling (biking). This is measured in steps (or rotations, if cycling) per minute. For most recreational runners and cyclists, cadence tends to be slower than professional athletes. One way runners and cyclists can improve is by increasing cadence.
The bike speed and cadence sensor is needed to measure cadence when cycling.
A foot pod is most often required when running. The lone exception is Garmin’s new Forerunner 620 which can measure cadence using its built-in accelerometer.
A few GPS watches are equipped with a temperature sensor. Except for the Garmin fenix, which can be paired with an external temperature sensor, these measurements aren’t all that accurate as they are skewed by body heat.
This is an intensity measure created by Firstbeat that’s available in two Garmin watches, the Forerunner 610 and Forerunner 910xt. By combining personal info (age, weight, height, gender) with your max heart rate, these watches will use your exercising heart rate and assign a training effect number between 1 and 5. Essentially, this number tells you the impact your workout had on your overall aerobic fitness. Check out more information here.
Swim Stroke and Lap Counter
One watch – the Garmin Forerunner 910xt – uses a built-in accelerometers to count swim strokes, laps, and swimming distance. Integrating the accelerometer allows a more accurate distance measurement when swimming indoors and better tracks distance outdoors without using the bathing cap method.
Indoors, pool size can be set, so as laps are counted, distance and speed are calculated. Outside, the accelerometer is combined with sporadic GPS signals (during the momentary seconds when the watch arm is above the water) to roughly determine distance.
Strokes are counted with the accelerometer. These watches also promise to determine which stroke you are using (crawl vs. butterfly, etc.), although reviews suggest this feature works rather poorly.
Ground Contact (Garmin feature)
Available on the Garmin Forerunner 620 (when used with the new HRM-Run monitor), ground contact is the amount of time your feet touch the ground during each stride.
Similar to cadence, ground contact gives you an idea of how fast your legs turnover. Generally speaking, the less time your foot touches the ground, the faster your cadence and the better your form.
Vertical Oscillation (Garmin feature)
Another new feature found on Garmin’s Forerunner 620 (also requiring the HRM-Run monitor) is vertical oscillation. This tracks how much you “bounce” up and down while running. It works by measuring the number of centimeters your core moves off a fixed point.
Up and down movement wastes energy while running; this feature should help improve form by tracking inefficient running motion.