Signedembossed on right black panel of adding machine: C.E. LOCKE / MFG. CO / KENSETT, IOWA / U.S.A.
embossed on left black panel of adding machine: LOCKE / ADDER / PATENTED DEC. 24, 1901
FunctionThis calculator performs addition operations. Users input desired numerals by lining up the border between the two colors on certain bars with the desired numeral on the black bar below. The resulting sum will be displayed in the windows on the front at the right of each bar. The Adder was notoriously difficult to use.
A complete discussion of the history, design, use, and advertisement of the Locke Adder is available here.
The original instructions for using the Locke Adder are available here.
Primary SourcesC. E. Locke Mfg. Co., "The Locke Adder Instruction Booklet" (Kensett, Iowa, 1902).