soofsoof says:Yes, I use the polar s150. Its main features are for running and cycling but it works perfect under water (for both running in the cold and swimming I use a cream to increase electrical induction).
As a matter of fact, the polar is a great swimming tool as I, at least, find it hard to estimate my effort while swimming and the polar really helps me stay in zone.
As for the distance, I count laps (pools)...