Turn the focimeter on

Turn the power wheel into the plus, then slowly decrease the power until the focimeter target (sphere and cylinder lines as seen in Figure 2) is sharply focused. Do not oscillate the wheel back and forth to find the best focus. The power wheel should read zero if the instrument is in proper calibration. If the power wheel does not read zero, re-focus the eyepiece and re-check the calibration. If the power wheel still does not read zero, the error must be compensated for on all future measurements made with the lensometer, or the lensometer needs maintenance.

Check Power Calibration

Ensure the power calibration of your focimeter is accurate. This should be done occasionally.