His 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.

Since 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.