The Antikythera mechanism suggests quite a bit of previous art. Making a device for counting wheel rotations wouldn't be very difficult. You could do the billin

The Antikythera mechanism suggests quite a bit of previous art. Making a device for counting wheel rotations wouldn't be very difficult. You could do the billing on a wheel too! One set for each customer! But it would be easier to just do the billing by carving it into a clay tablet.