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Precise Adder

Precise Adding Machine - Precise Developments Co. Inc. Chicago IL U.S.A. 1946
Precise Adding Machine
Precise Developments Co. Inc. Chicago IL U.S.A. 1946

 
The Precise adder is a sturdy little adder manufactured by Precise Developments Co. of Chicago.
 
Here is a blurry video demonstration (note: audio is delayed several seconds)

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That protrusion is a brass stylus, conveniently stored in the undercarriage. It is used to engage the gear pins to dial the number desired, which is added to the result seen in the window.
 
An unusual aspect of the the Precise adder is the glass lens that sits across the result window and serves to magnify the digits seen there.
 
 
 The handle on the right clears the result to zero.
 
 

Precise Adding Machine Patent 2402549 O. R. Hartom Sheet 1 1946
Here is the drawing for the patent referenced on the machine's front plate
Patent 2402549 O. R. Hartom 1946