Eli5 What is the story with those 4 armed clocks at swimming pools lanes?

Question

Sometimes they have 4 arms of different colors. The markings with a marking every 5 minute mark, and bigger ones at the 15 , 30, 45, 60 markings…Clearly the markings represent increments of an hour

In: 3

Answer 1

> Clearly the markings represent increments of an hour

Yes, they are seconds.

The clock is called a “pace clock” and it is useful in swimming training. If someone wanted to time their laps it is convenient to have a clock that they can see when they start and when they end, and by having multiple arms they won’t need to wait very long in order to get to a good point of reference.

Multiple swimmers can be in the water at once and in order to avoid interfering with each other can delay their start times by 5 seconds for example.