The pace clock is like a big stopwatch, except that it runs continuously. it's used to time our swims, to time your rest intervals, and to keep you separated from the other swimmers in your lane.
The pace clock performs two important roles:
1) It allows you to perform interval sets during your swimming workout.
2) It is necessary in assessing your swimming improvement. The typical pace clock is really a very simple instrument to use. it has a minute hand and a second hand and is divided into 5 second increments from 5-60 seconds.