If you are trying to figure out the add in someone's progressives, there's no guesswork involved, it's written on the lens. See my page of progressive lenses for details.

Plus Lenses Rx +3.00 +4.00 Approx. +5.00 +5.50 and +6.00 Between +5.00 and +.6.00 +6.00 and +9.00 +8.50

Minus Lenses Rx Approx. -2.00 "old-style" Approx. -3.00 and -5.00 "old-style". -3.00 -3.75 Around. -4.00 or -5.00 with add. -8.50 -8.50 -15.00

For more pictures in higher strengths, please see our companion site GOC.org