Counts your pool lengths. Start Button: when presses you have 3 secs to start swimming before calculating pool direction. then starts detecting your turns. Stop Button: when swimming you can press stop, it will add 1 lap, as i thought you normally press stop when you reach the end! and it saves waiting for the watch to detect a direction change. Previous Button: change pool lengths 25m 33m 50m Next Button: Resets laps and distance (only when stopped Select Button: Manually add laps. It does show HearRate which on the FR 235 seems suprisingly accuraty for been under water but the text is too small to read so was added more as a novelty and practice fir my programming!