Locke Adder

Clarence E. Locke (1866-1945) from Kensett, Iowa, USA, was a holder of 2 US and 2 German patents for a calculating device—slide bar adder, which became popular as Locke Adder. The first patent is No 689680 from December, 1901, the second is No 779088 from January, 1905 (see the lower patent drawing).

The second patent drawing of Locke Adder

The Locke Adder (see the lower photo) is a row adder using alternating fixed and moveable horizontal bars, as carrying from one column to another is manual. The nine moveable slides show either red or green while in the zero position, and expose either silver or yellow as the slides are moved to the right. Between the slides are eight fixed bars, painted black with white numbers from 1 to 9. The sliding bars of hollow aluminum are manipulated with the fingers in order to determine sums.

The Locke Adder

A number is entered on a given bar by placing the index finger on the raised knob corresponding to the desired digit and sliding the knob leftward as far as possible. The user must account for a tens carry manually by a combination of a rightward adjustment of the current bar and the advancement of the bar above by one, much as is done with a traditional abacus. The split-colored sliders aid the user in recognizing and carrying out the tens carry operation.

The Locke Adder was a very beautiful, but not a user-friendly calculator. It enjoyed a modest (albeit brief) success, thanks to a low price and an extensive print advertising campaign in the first few years of the 20th century (see the lower image). It was on the market for less than ten years, probably being supplanted by dial adders such as the Calcumeter and the Calculator. The machine was manufactured by the company of his creator—C. E. Locke Manufacturing Co., Kensett, IA. The prices were: 1901-05 Price $5; 1906 Price $5 (oxidized copper finish) and $10 (oxidized silver finish with case); 1908 Price $5 & $10.

The Advertisement for Locke Adder from 1901 in The American Monthly Review