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Prototype Ridley Slide Rule
CONTACT LENSES AND ACCESSORIES
slide rule
Keeler
Europe: United Kingdom
1948
plastic; (box) wood
overall: 11 x 662 x 58 mm; box: 25 x 690 x 76 mm

White plastic slide rule with printed scales and additional scales marked in ink on paper attached by tape. Upper scale calculated for a refractive index of 1.336 (tears) giving the power of the back curve of the lens in the eye for any nominated radius. Lower scale calculated for a refractive index of 1.490 (contact lens material). Transparent cursor. In hinged wooden case with two yellow metal clasps.


2003.2

Ex Keeler Collection



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