The operation is the following: a mechanical clock makes make a full rotation with the central disc. Every four hours, a hole lets pass a ball which fall into the basin from the bottom. This ball symbolizes glass which one has the right to drink. Thus six balls fall each day, the six authorized glasses...
But we are not obliged to drink them!
If that arrives, one can deposit the supernumerary ones in the higher basin
and thus constitute a small bank which could be useful in the event of
imprévu. By respecting the values that one had asserted.