Quote Originally Posted by onthegrind View Post
Ans for Ques 17 is a) 71mm. Reason: MBS = (frame PD/geometric center distance - person PD) + ED. mbs = ((54 +16) - 64) + 64. mbs = (70-64) + 64. mbs = 6 + 64 = 70. 71mm is within 1mm tolerance

Nope. You didn't account for the 1.5 diopters of base in prism in the Rx. You'd decenter each eye OUT from the PRP/Patient PD to induce the prism, making the blank requirement 6mm LESS than what you calculated.