Origin of modern calculating machines

by J. A. V. Turck

Blaise Pascal

The pounds register-drums, or numeral wheels, are each operated by a train of gearing connecting them with a ten-armed turnstile wheel which form the hub and spokes of what appears to be a series of wheels on the top of the casing. While the spokes and hub are movable, the rims of these wheels are stationary and are numbered from 1 to 9 and 0.

The geared relation between the turnstile wheels and the numeral wheels is such that rotating a turnstile will give like rotation to its numeral wheel.

Assuming that the numeral wheel of any one of the different orders registered 0 through its sight opening and the turnstile of the same order was moved one spoke of a rotation, it would move the wheel so that the 0 would disappear and the figure 1 would appear; now if we should move the same turnstile three more spokes the numeral wheel would move likewise three spaces and the 4 would appear.

A stop in the form of a finger reaching over the spokes is provided to stop the turnstile at the right point so that the figures on the numeral wheels may register properly with the sight openings in the casing.

Constructional features of the Pascal machine

The figures on the wheel rims fast to the casing are arranged anti-clockwise to register with the space between the spokes, the 0 registering with the first space, the 1 with the second space and so on around the wheel. Thus by use of the finger or a stylo inserted in a space opposite the number to be added, the operator may move the spoked wheel or turnstile clockwise until stopped by the stop finger. By repeated selection and operation for each figure to be added, the wheels will be revolved through their cycles of rotation caused by the accumulation.

As the numeral wheels complete each rotation the 0 will appear, so that a registration of the tens must be made. Pascal provided for the accumulation of the tens by automatically turning the wheel of next higher order one point through the action of the lower wheel.

The novel means employed for this transfer of the tens consisted of a one-step ratchet device operated by a pin in the train of gearing connected with the lower numeral wheel, which, as the lower wheel passed from 9 to 0, forced the lever to which the ratchet pawl was attached in a direction to cause the gearing of the higher numeral wheel to be ratcheted forward far enough to add one to the higher numeral wheel.