1. Determining lens centration
Mark the geometric centre with a vertical line using the boxed lens system.
2. Preparing the measuring aid
Setting knob (1) back, measuring arms (2 and 3) closed. The setting knob is easy to use.
3. Place the measurement aid on the frame
When you place the measurement aid on the frame the measuring arms open. Ensure the guide bar (4) is apposed to the upper edge of the frame. The mid marking of the guide bar accords with the frame midpoint.
4. Adjusting for horizontal inclination
Adjust the measuring arms (2, 3) by moving the setting knob forward. When the measuring arms rest on the lens marking they are at the correct angle.
5. Reading the horizontal inclination
Read the angle at the point where the measuring arm accords with the scale.