Comptometer in Room 506
The comptometer was the first commercially successful key-driven mechanical calculator. Although the comptometer is primarily an adding machine, it can also do subtraction (making use of the 9’s complement method), multiplication and division. The comptometer is extremely fast because each key adds or subtracts its value to the accumulator as soon as it is pressed and a skilled operator can enter all of the digits of a number simultaneously, using as many fingers as required, making them sometimes faster to use than electronic calculators. Consequently, in specialized applications, comptometers remained in use in limited numbers into the early 1990s.
The Model H comptometer (SN 208336) in Room 506 was donated by two LASA students in 2024, whose great-great-great uncle Dorr Eugene Felt was its inventor. The Model H (SN 200,109 to SN 244,975) weighs 21 pounds and was manufactured in Chicago from 1920 to 1926. They’re not so easy to come by as many units were melted down for bullets during wartime.
Original Manuals Model-H Easy Instructions Methods of Operating