How Do You Know Your Lens Is The Right Power? (Part Two)

Practical Advice for Checking Focimeter Consistency and Calibration Drift

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In Part One of this three-part series, I described the history and early use the American Optical (AO) “NBS Truepower lens set” developed in 1916, which was used to assess the calibration of the AO Lensometer when first introduced to the market.

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