When I was at school (a long time ago), they tried to explain computers to us by making an adder using beads and matchboxes. We didn't have classroom computers

When I was at school (a long time ago), they tried to explain computers to us by making an adder using beads and matchboxes. We didn't have classroom computers back then. I'd like to know how that worked. I've always wanted to build a digital clock entirely running on fluids. It would use fluid gates, and present a digital display by pushing blobs of coloured immiscible liquids back and forth through glass tubes (perhaps arranged as a seven-segment display). The counter itself would be made using fluid gates (which I don't know how to make). It would be slow; but for a wallclock with minute precision, you hardly need nanosecond gates. So I wish "fluidonics" were popular.