How We Tested GPS Sports Watches

By:
Jediah Porter and Joanna Trieger

Last Updated:
Thursday
June 7, 2018
Lead test editor Jediah Porter putting devices (and his cardiopulmonary system…) through the paces on an uphill interval session.
Lead test editor Jediah Porter putting devices (and his cardiopulmonary system…) through the paces on an uphill interval session.

To see how these products tracked athletes' movement, we covered some ground. We logged thousands of miles, mainly on foot. Whether those feet were in running shoes, mountaineering boots, or backcountry ski gear, our testing was real-world and comparative. We would regularly wear and compare multiple contenders on the same endeavor. However, to truly get a feel for each device we made sure to use each one exclusively for at least a week of training.

We included several editors in this review to capture different perspectives on what makes an outstanding GPS watch. For several years, our lead tester tackled his most ambitious training regimen ever, logging an average of seventeen training hours a week for one 40-week period. He also visited six countries on two continents and traveled more new-to-him miles than in any other period of his life. The lead tester monitored virtually every one of his training and active hours with one or more of the products in this review. For our 2018 update, our testers wore the devices 24/7 as they trained for the San Francisco Marathon and the Downieville All-Mountain races, averaging seven to eight training hours each per week.

After this much use, only a few objective comparison tests were necessary. Specifically, each tested model was used to measure the distance on a known track to assess accuracy. Also, we made sure to run each GPS watch tested from full to zero battery to compare it to the manufacturer's claim of battery life.

Ease of Use


By simply using the devices, and sharing them with a broad and deep test team, we developed and distilled a significant body of user experience. We back up our opinions with years of experience and at least weeks, usually months, of using each device.

The Forerunner 645 Music is easy to navigate  here a tester quickly checks his heart rate following a run.
The Forerunner 645 Music is easy to navigate, here a tester quickly checks his heart rate following a run.

Features


We compared each product to a list of potential features. Our list of features is a combination of hardware and software. Some devices can be customized further. The list of potential features we compared are timekeeping, GPS distance, and speed, GPS data recording, GPS navigation, step count, sleep tracking, built-in heart rate, compatibility with external sensors, barometer, altimeter, thermometer, and smartwatch functions.

Accuracy


We evaluated each device's GPS distance measurement on a standard running track. Each device was subject to at least two test rounds of half a mile each. Reported inaccuracy is the average percent deviation of the watch results from the actual distance. We also tested the accuracy of the devices that include altimeters by first calibrating them using GPS (if available) and noting the variation from our known elevation. We then calibrated them manually to our known elevation, traveling to a NOAA survey marker, and reporting the variation from the surveyed elevation.

Ease of Set-up


In configuring each device, we monitored the steps required, the clarity of device, app, and paper instructions, and the time required, including active time setting up and passive time awaiting initial sync.

Battery Life


A wide range of variables makes it challenging to test the battery of GPS watches objectively. We gathered anecdotal evidence while using each device, weighing our impressions against each devices' intended niche. In our 2018 update, we got a little more scientific, using each device in our test group to GPS track the same activity from fully charged until their batteries ran out.

The batteries of the Garmin Forerunner 935 and the Garmin Fenix 5 lasted so long  we had to drag them into the office the day after we began our continuous GPS test. The Fenix 5 (right) bit the dust shortly after the 20-hour mark  while the Forerunner 935 lasted past 21 hours.
The batteries of the Garmin Forerunner 935 and the Garmin Fenix 5 lasted so long, we had to drag them into the office the day after we began our continuous GPS test. The Fenix 5 (right) bit the dust shortly after the 20-hour mark, while the Forerunner 935 lasted past 21 hours.

Portability


Mainly, portability is a function of size. Larger watches are less portable and smaller ones are more portable. We measured and weighed each one, and noted whether they were difficult to wear under typical running and athletic clothing.