Originally posted by Darryl Meister:
1. You need to know the index of refraction of the lens material. This isn't always the easiest thing in the world to determine.
2. You need an accurately calibrated lens clock. You also need to use the lens clock correctly (e.g., holding it perpendicular to the surface).
3. You need to caliper the lens thickness if the lens is plus-powered.
4. You need to determine the minimum and maximum surfaces powers on the toric back surface, if the lens has cylinder power. You may also need a protractor or something to establish the correct axis.
5. If the lens is aspheric or progressive, lens clock readings will not be accurate.
Best regards,
Darryl[/I]
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