These Grasslin Clock Switches are typically used on Chlorinators which before more easily accessible technologies became available. would naturally suite mechanical clock switches.
Of course the clock is powered by electricity, if you listen carefully you can here a sort of motor whirring. There are sort of mechanical hours and half hours on the dial that you push in and to start and stop the pump.
You may be surprised by how tricky and simple this Grassline Time Clock Switch can be to at the same time.
The Graesslin Websites is here https://www.graesslin.de/en/time-switch-technology
A couple of interesting YouTube videos.
Grasslin Pin Time Clock