Without the right vision equipment, it may be hard to tell if eye glasses have been improperly calibrated. Eye glass lenses are measured by four major optical properties: the axis, sphere, cylinder and focus values. The axis values measure the required amount of rotation needed for a person with an astigmatism. Astigmatism can be corrected by adjusting the axis of your eye glass lenses to eliminate headaches or distorted vision at near-sighted or far-sighted distances.

Mount the eye glasses against the base of the lensometer platform.

Center one of the lenses in the optical viewfinder of the lensometer. The axis is measured by criss-crossing narrow lines that will become parallel when the axis are aligned. Begin turning the axis knob to make the viewfinder's lines parallel.

Measure the readings on the axis knob. The measurement value represents the axis for the eye glasses. Repeat steps 1 to 3 to find the axis for the other lens.