Hey macchiat@

Dont know exactly i just like to take photos :) thanks for asking though

But you have to "charge" it with the wooden handle on the right once a day. I think the stones and a spring must play a role..

If you have a spring pressed in, it wants to extend back again. So that is whats probably create a "force" and the stones most likely functions as a contra-weight. I could be totally wrong. Im not very technical last thing i studied was bookkeeping. 😎