Brunsviga 13RK
From Wiki
Brunsviga 13RK
- Type: Mechanical Calculator
- Size: 12"W x 10"D x 7"H / 30 cm W x 25 cm D x 18 cm H
- Material: Steel
- Serial Number: 34-93178
The pinwheel calculator was invented in the late 19th century and was the standard desktop unit in financial offices until the 1960s. The "pinwheels" were the drums at the heart of the calculator. The drums were set by little tabs and then rotated by a large crank to add and subtract to an accumulator. A third register counted the number of times you cranked the crank and the accumulator could be shifted to the left and right. These features allowed for quick multiplication and division. For division there was a bell that rang whenever there was a carry/borrow out of the accumulator. (Division was by staggered repeated subtraction. Just crank the crank backwards until the bell rang. The bell told you you underflowed the accumulator. One forward crank after that would eliminate the underflow. You then shifted the accumulator and started cranking again.) The 13RK included a "register transfer" feature that moved the value in the accumulator into the input register, setting the drums for the next calculation.
Negative numbers were not supported. The sudden appearance of a large number of 9 digits (and a bell ring) alerted you that you had underflowed the accumulator and might have acquired a negative number. You'd have to deduce the correct value using nine's-complement arithmetic.
Brunsvigas were made by Brunsviga Werke in Braunschweig, Germany, home of my favorite lunch meat. They merged with Olympia Werke in 1959 and this model was discontinued around 1964.
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