Pinwheel Mechanical Calculator

This exhibit represents a pinwheel calculator, a widely used class of mechanical desk calculator during the first half of the twentieth century. Such machines supported numerical work in engineering, science, commerce, and government. Their registers store decimal digits as mechanical positions; the exhibit requires no electronic arithmetic.

The mechanism, left bare:

① Each setting lever extends 0–9 pins on its pinwheel, encoding the selected digit mechanically. ② One crank revolution rotates the rotor; extended pins engage the counting mechanism and advance the corresponding result drum. ③ A transition from 9 to 0 actuates a carry lever, advancing the next decimal position. ④ The revolutions register counts crank turns, while shifting the carriage changes the decimal place at which the rotor acts.

Operation: a forward turn adds the rotor setting and a reverse turn subtracts it. Multiplication uses repeated addition by decimal place: for 271 × 38, set 271, turn eight times, shift one place, and turn three times. One common division procedure repeatedly subtracts at each place until underflow actuates the bell, restores one turn, and then shifts right. The quotient is accumulated in the revolutions register. The Auto controls demonstrate these modeled procedures step by step.

Drag to orbit · scroll or pinch to zoom · tap a lever knob to bump that digit.

Pinwheel kinematic reconstruction with six input digits. Gear profiles, spacing and counter linkage are simplified; this is not a dimensioned replica. Amber: input pins. Blue: star wheels. Ivory: number drums. Coral: carry fingers and latches.