You can consider this installment four of my previous question which is the third installment.

Throughout history, we have developed many methods of telling time. The most famous two examples being the clock and the sundial. The ancient Egyptians invented the clepsydra, an extremely simple device that uses dripping water as a way to tell how much time has passed. There are also, for example, hourglasses, which flow sand as a measurement of time.

Suppose, though, you were an intelligent dolphin and, for some reason, had to always have a time reference on you. Being under the water seems to present a challenge, for technology like clocks and hourglasses don't seem to be possible to make under the water, a clepsydra certainly wouldn't work since you can't pour water underwater, and a sundial wouldn't have the proper lighting. So you must improvise in order to find a way to keep track of time. How would you improvise in order to keep track of time.