In reply to the sheep:
Most competitive swimmers don't wear watches .They are quite poor at counting lengths. It's really annoying when you are sure you've done 400m and the watch insists you've done 350, or worse 375!
Running is a different matter, and most people find garmin a good brand, others use suunto or Tom Tom, though the latter isn't really in the market seriously any more. Most of These will also do pool length counting with varying success.