Trying to keep costs down. I have a garmin gps watch with an auto lap ability. Has anybody ever tried using this method before?

 

I tried it once with my Garmin Edge 705 and had pretty bad results.

Not sure if there was major interference from all the cars running timing beacons or something else on track, but the gps data was really poor and just skipped between points on track making for inaccurate lap times. Pretty much made it impossible for the auto lap function to work.

Even when I tried hitting the lap button myself I got skewed results.

 

Damn I only have a 305 forerunner. If an edge 705 can't do it. oh well.

 

What's the sampling rate of the 305? I believe it's only 1 Hz. If so, you're speed is far too high to get useful results.