Patent:GB191210855

"Adding and subtracting apparatus. For calculating dates, a wooden or other base has two grooves and is divided on back, front, and ends into 365 parts numbered from unity in each direction. In each groove slides a strip also divided into 365 parts and inscribed one, 13, with the month and days of the month, the other, 14, with the days of the week. " (aus der Patentschrift)

• DATUM: 28.11.1912
• TITEL: Improvements in Date Calculating Devices.
• PERSON: KERR DAVID SMITH CA

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