What is a "lap" in swimming and how could it be different from a "length"?

Lap and length are interchangeable. They are equating it with running where a lap is one unit around a track, as a length is one unit across a pool. It exists because it is a running watch that they threw some swimming stuff into. The difference in one lap or length is likely due to how it counts the final lap/length. It is using the accelerometer to try and figure out when you are reaching for the wall to turn, but you need a very strong turn to trigger it. It also counts after the first turn, so the total is the laps completed so it will always be one short until the end. It is likely you did not register the final lap as you probably coasted to the wall. Make sure on the final lap that you have a strong finishing motion, so it registers the movement.

I hope this helps answer your question. If so, please mark it as a solution so others can look for it if they have the same question.

JohnHorner wrote:

Your theory makes sense … if I had 16 lengths and 15 laps. But what I had was 16 lengths and 17 laps.

Also, if the watch counts both laps and lengths using the same method (reaching for the wall/strong turn etc), how would they ever be different?

They would be different because the watch is not really very good at tracking swimming. Frankly, I am amazed you are only off by 1!