This is an Odhner-type pinwheel calculator — the standard desk machine of the 1930s–40s (Original-Odhner, Brunsviga, Felix). Wartime "computers" were people in ballistics, engineering and logistics offices turning cranks on machines exactly like this one. There is no electricity anywhere: every digit is a gear position.
The mechanism, left bare:
① Each setting lever extends 0–9 brass pins on its wheel — the number you keyed in is literally stored as protruding metal. ② One turn of the crank spins the whole rotor; the extended pins mesh through the pinions and push each ivory result drum forward exactly that many teeth. ③ When a drum rolls past 9 to 0, it trips the red carry lever, which kicks the next drum one extra step — watch the carries ripple leftward late in the turn. ④ The black revolutions register counts your turns; the carriage slides sideways so a turn lands at ×10, ×100…
Operating it: addition is one forward turn; subtraction one reverse turn. Multiplication is repeated addition: for 271 × 38, set 271, turn 8 times, shift, turn 3 times. Division is done by feel: subtract at the highest place until the bell rings (you overdrew — the register shows the tens-complement), give one turn back, shift right, repeat. The quotient appears in the revolutions register. The Auto buttons perform these exact historical procedures, turn by turn.
Drag to orbit · pinch or ⌘/Ctrl + scroll to zoom · tap a lever knob to bump that digit.
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