Quote Originally Posted by Lise
What does the "50" refer to?
Meters. An Olympic sized pool should be 50m long, but many smaller pools will be 25m.

When I was on swim team years ago, we had a gigantic clock next to the pool. When training we would do a lap starting every 60 seconds, so you'd launch off at the 0 second mark every time, finish your lap, and then start again. They were like mini-intervals. Then afterwards you would know how many laps you'd done by how many minutes you'd been going.

As for long stretches, I always did the longer 500m events (20 laps in a 25m pool) and I don't remember having problems keeping track of laps. I would just repeat the current number in my head over and over again through each lap.