Abstract
The accuracy of 26 aged and three new lens measures was investigated. Instruments were applied to surfaces of known curvature employing the conventional, hand-held method as well as while rigged on an optical bench. In addition, using the latter method, a controlled amount of surface tilt was introduced. A large inter-instrument variation in accuracy was encountered. In general, hand-held lens measures were found to provide equally accurate measurements on convex and concave surfaces, with the exception of the −20 D surface, and inclinations from 0° to 5° did not result in erroneous measurements. Results for inclinations of 15° became unreliable. The different usages of the instrument are discussed.
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