Following on from earlier posts - it is a pace clock for swimming. Typically people wait for the pointer to hit zero (ie 12 O'clock) then swim a given distance (ie a length of the pool) andcheck the clock to see how long they took. To save having to wait for the pointer to reach zero - for example if it is at 05 - there are four different coloured pointers at 15 second spacing. Then swimmers just have to wait for the *red* (or whichever) pointer to hit zero - so only need wait 15 seconds max. Also useful if four people want to measure pace in a group.