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An adding machine is a type of calculator, usually specialized for bookkeeping calculations. In the United States, the earliest adding machines were usually built to read in dollars and cents. Adding machines were ubiquitous office equipment until they were phased out in favor of personal computers, beginning in about 1985. The machines were rarely seen after the year 2000.

Blaise Pascal invented the mechanical calculator in 1642;[1] it could perform additions and subtractions directly and multiplication and divisions by repetitions. He was followed by Thomas de Colmar who launched the mechanical calculator industry in 1851 when he released his simplified arithmometer (it took him thirty years of development to turn his complex multiplying machine, patented in 1820, into a simpler and more reliable adding machine). However they didn't gain widespread use until Burroughs and Felt introduced machines in the 1880s.[2] It came out in 1888.

## Contents

### Operation

To add a new list of numbers and arrive at a total, the user was first required to "Zero" the machine. Then, to add sets of numbers, the user was required to press numbered keys on a keyboard and then pull the crank. This caused the numbers to be shown on the rotary wheels, and the keys were released in preparation for the next input. To add, for example, the amounts of A£30.72 and A£4.00 (which, in adding machine terms, on a decimal adding machine is 3,072 plus 400 "decimal units"), the following process took place: Press the 3 key in the column fourth from the right (multiples of one thousand), the 7 key in the column 2nd from right (multiples of ten) and the 2 key in the right hand (multiples of 1). Pull the crank. The rotary wheels now showed 3072. Press the 4 key in the 3rd column from the right. Pull the crank. The rotary wheels now show a running 'total' of 3472 which, when interpreted using the decimal currency colour coding of the key columns, equates to A£34.72. Keyboards typically did not have or need "0" (zero) keys. Trailing zeros (those to the right of a number such as the one to the right of the 3 in the example), were there by default because when a machine was "Zero-ed", all numbers visible on the rotary wheels were reset to zero.

Subtraction was impossible, except by adding the complement of a number (for instance, subtract A£2.50 by adding A£9,997.50).

Multiplication was a simple process of keying in the numbers one or more columns to the left and repeating the "addition" process. For example, to multiply A£34.72 by 102, key in 3472, pull crank, repeat once more. Wheels show 6944. Key in 3472(00), pull crank. Wheels now show 354144, or A£3,541.44

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. Multiplication was similar to that on the adding machine, but users would "form" up their fingers over the keys to be pressed and press them down the multiple of times required. Using the above example, four fingers would be used to press down twice on the 3 (fourth column),4 (third column), 7(second column) and 2 (first column) keys. That finger shape would then move left two columns and press once. Usually a small crank near the wheels would be used to zero them.