Mannheim slide rule, 20 1/2", by Keuffel and Esser Co., in dilapidated case Mannheim slide rule, 20 1/2", by Keuffel and Esser, with case
Engineer's slide rule 15" D R Patent No. 173660 in black card case Mannheim-type scales on front, engineers' constants on back Engineer's slide rule 15" D R Patent No. 173660 in black card case Mannheim-type scales on front
Mannheim box-wood slide rule (26 cms) with cursor, made by Tavernier-Gravet (Paris) Mannheim box-wood slide rule (26 cms) with cursor
