Orthops Slide Rule

Historical Significance: Various rules for the measurement of facial and spectacle frame dimensions were devised in the 1930s. This reflected the desire of early 20th C optometrists and opticans to be as precise as possible in fitting spectacles. The British Optical Association Museum has two paper items that give a description of this rule and its use. See Cat No 1940 for instructions for its use. See Cat No 1931 for another later version of this rule made with plastic rather than wood, This is a duplicate of Cat No 1949. The book L S Sasieni Spectacle fitting and optical dispensing 1950 (Cat nos 776 )2243) has an informative chapter (ch 2) on frame rules and one (ch 5) on devices for face measurements.