I run intervals at an asphalt track at what was once a middle school. I am trying to figure out whether or not my GPS watch is malfunctioning. I purchased a Garmin because when I compared it to a Suunto, the Garmin's mileage was more conservative. The Garmin would come up as .99 or sometimes .98, and the Suunto would be at 1.00. Hence, I have always thought my Garmin Forerunner 10 to be a little conservative, which is fine.
Today though, and recently in general, my Garmin has made me "fast." I am now wearing both a regular sport watch and a GPS watch at my workouts--the watch to time rest/jog portions, and the GPS for overall timing and distance, including my warm-up and warm-down mileage. I was supposed to be hitting 4:29 for my 1200s today (6:00) pace with 400m jogs in between. While it did progress downward throughout the 4x1200, the best I ran was 4:31 (last) and my first interval clocked at 4:40.
I did some math, and saw that a 1/4-mile track (compared to a 400m track) could add 10-12 seconds per mile, depending upon pace. Still, the Garmin had me at 6:06, 6:07, 6:04, 6:06 for the 4-mile up-tempo splits...yet as per my sport watch I averaged 4:36.4 (about 6:10) for the four 1200s. For example, I was 4:40 + 1:51 for the two portions, speed and jog, for my first interval pair. Together, that would make for a 6:31 pace. Why would the Garmin say I was 6:06 in that first mile? That seems way off.
I would have to say that in the 1.5 years or so that I have had the Garmin, it would seem to have been accurate.
What gives here? Am I missing something? Do I need a new GPS watch?
Thanks...