

Device for Calculation: An early version of today's complicated
calculator, Leonardo's mechanism maintains a constant ratio of ten to one
in each of its 13 digitregistering wheels. For each complete revolution
of the first handle, the unit wheel is turned slightly to register a new
digit ranging from zero to nine. Consistent with the ten to one ratio, the
tenth revolution of the first handle causes the unit wheel to complete its
first revolution and register zero, which in turn drives the decimal wheel
from zero to one. Each additional wheel marking hundreds, thousands, etc.,
operates on the same ratio. Slight refinements were made on Leonardo's original
sketch to give the viewer a clearer picture of how each of the 13 wheels
can be independently operated and yet maintain the ten to one ratio. Leonardo's
sketch shows weights to demonstrate the equability of the machine. 
