Holman Adding Machine. This round metal patent model for an adder with carry has a cylindrical case that contains two concentric rotating rings, each with the digits from 0 to 99 engraved evenly around the edge.

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Size: 1961px × 1275px
Photo credit: © SBS Eclectic Images / Alamy / Afripics
License: Licensed
Model Released: No

Keywords: mathematics, medicine, science