Many manufacturers offered "pair" rules. Normally a pair consists of 10 inch and 5-inch rules having the same scale set. Supposedly, 10 inch rule was used at desk, whereas 5-inch rule was for "mobile use". Having the same scale set, one can carry out calculations in exactly the same way. I suppose there were many engineers who had several rules, But the ones who bought "pair" rules must have had clear conscience and pride to be engineers.
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Faber Castell 2/83N and 62/83N
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Hemmi 259D and 149A
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Keuffel & Esser 68-1100 and 68-1130(Deci-Lon)
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Keuffel & Esser 4181-3 and 4181-1
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Keuffel & Esser N4092-5 and 4092-3
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Pickett N3 and N3p
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Pickett N803 and N600
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Post 1460 and 1461
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