Tuesday, September 1, 2009

Garmin Forerunner 310XT swim accuracy

I've owned my Garmin Forerunner 310XT for just over a month now, and the thing that has frustrated me most has been the accuracy of the 310XT on the swim.

See, I'd owned the Garmin Forerunner 305 for a year and really enjoyed using it to track my on-land legs of triathlon training and racing.

So when I saw the 310XT coming out, I knew I had to have it, even though the 305 was still functioning just fin. Imagine, I thought, with the 310XT I could track just how much I drifted off-line in the open water swims!

So, imagine my dismay when I wore my 310XT for the whole race in a sprint triathlon, and the map at right is how the 400m swim looked when uploaded to Garmin Connect. (click it to get to the activity details on GC)

Say what? I know for a fact I didn't do any loop-dee-loops on the swim course, and while my sighting is bad at times, there's no way I'm that jagged in a swim. And a half mile course? I don't think so.


So I gave the 310XT another try on an open water swim training over in Redwood Shores that I knew to be one mile long. As you see in the map at left, the jaggies were back, and while the time was good (just over 30 minutes), the distance was incorrectly logged at 2.15 miles. Again, click the map to get the activity details on GC.


So, before participating in the Silicon Valley Tri Club's practice session for the upcoming Santa Cruz Triathlon, I decided to consult the internet to see how to make the 310XT more reliable on the swim.

The verdict? Tuck the 310XT under your swim cap. Not at the top of your head, but at the back of your head, so when you're looking down in the water, the GPS unit is facing up. And lo and behold, it works!

Take a look at the map on the right, and you'll see just how smooth the path is (yes, I'm proud of my sight lines) and the distance accuracy is so very close to perfect as well! (with 10% which is a great improvement over the +100% accuracy of wearing it on my wrist).

By tucking the 310XT under your cap, the timing of the distance is a little longer than it should be what with turning it on before putting your cap on, but the accuracy of both distance and path can't be beat.

I'm now pleased as punch that I can more accurately track my sighting abilities on my open water swims using the 310XT.

Next thing to conquer? Getting the damn thing to pair to my Garmin Heart Rate Monitor that I've been using with my 305. Always something to tinker with!

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