machines consisted of several wheels (6, 8 or 10) with
the numbers 0 to 9 on each, closely resembling a telephone
dial. Two features merit special note. One, the carry
mechanism and two, his > use of complement arithmetic
for subtraction. The carry was performed by a weighted
ratchet which gradually stored energy as it approached
9. When it passed from 9 to 0, the ratchet was released
and in falling transferred a unit to the wheel of the
next higher order.
the wheels could only go clockwise, there was a second
set of numbers on the wheels going in the opposite direction,
and subtraction was done by complement arithmetic.