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

Practical Advice For Checking Focimeter Consistency And Calibration Drift

I was fortunate to have access to the NBS 1916 calibration set, from which I was able to make my own secondary set, which I still use today. Since I had confidence in their powers, it has proved especially useful. What does one do if there is a need to assess an instrument but one does not have such a set?

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