Adding Machine

An adding machine is a type of calculator. Usually this sort of calculator is specialized for bookkeeping calculations.

In the United States, very old adding machines were usually (always?) built to read in dollars and cents. They required the user to pull a crank to add numbers. The numbers were input by pressing keys on a large keypad: for instance, the amount $30.72 was input using keys corresponding to "$30", "70¢", and "2¢", and then pulling the crank. Subtraction was impossible, except by adding the complement of a number (for instance, subtract $2.50 by adding $9,997.50).

A later adding machine, called the Comptometer, did not require that a crank be pulled to add. Numbers were input simply by pressing keys. The machine was thus driven by finger power. Some adding machines were electromechanical -- an old-style mechanism, but driven by electric power. Some "ten-key" machines had input of numbers as on a modern calculator -- 30.72 was input as "3", "0", "7", "2". These machines could subtract as well as add. Some could even multiply! These old machines could be a royal pain to maintain and often gave wrong answers. It was probably better to learn to use an abacus. Modern adding machines are like simple calculators. They often have a different input system, though.

To figure out this:	Type this on the adding machine:
2+17+5=?	2 + 17 + 5 + T
19-7=?	19 + 7 - T
38-24+10=?	38 + 24 - 10 + T
7×6=?	7 × 6 =
18/3=?	18 ÷ 3 =
(1.99×3)+(.79×8)+(4.29×6)=?	1.99 × 3 = + .79 × 8 = + 4.29 × 6 = + T

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