Can anybody help me. I trying to do an accurate thickness calculator on excel, as my current surfacing calculator doesn't handle finished plus lens thickness very well for rimless and supra.

Since I surface I know the base curve, the minimum size uncut and the finished edge thickness. So to ensure that the back vertex power is correct I need to know the thickness of the lens first. But to calculate the thickness I need edge thickness, sag1 and sag 2. So how do these surfacing programs work do they have an average thickness for a given base in a given lens power and index? Or do they have an average back surface power for a given base, lens power and index?

I thought one way to do it acurately was to calculate the approximate thickness using the approximate sag formula then sag 2. Then simply work it back through to find the accurate thickness using accurate sag formula?

Is there an easier way?

Confused.....

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