Patent:GB191512793

"Proportional calculators.-Percentage-computing devices comprise a box provided with a lid having parallel but unequal ends b, b<1> divided into the same number of divisions and connected by coloured or other lines d'. Adapted to lie across the lines d<1> and to move parallel to itself is a second scale c, of which a variety is provided. The divisions in the scales b, b<1> are oppositely numbered. Any desired percentage of any value upon the second scale may thus be determined...."

• DATUM: 07.09.1916
• TITEL: Improvements in Devices for Calculating Percentages and the like.
• PERSON: HARVEY CHARLES JAMES

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