Forerunner 910XT and Garmin Swim utilizes arm movements and preconfigured data (such as pool size) to provide swim metrics.
Discrepancies in distance may be caused by multiple sources:
To decrease the amount of discrepancies:
As swimming technique improves with the use of the above instructions, distance accuracy will improve.
1 - If drill log is not available; utilize rest intervals for drills that affect arm movement
2 - If lengths are being missed (under-counted) in a small pool, consider utilizing a standard-sized pool as the watch may miss lengths for strong swimmers who only take a few strokes to cross small pools