# Optical Forums > Ophthalmic Optics >  Image jump-please help

## benice

hi can anyone help me with this question please?

calculate image jump for:
CR-39 flat top (distance from segment OC to segment top= 4mm)  add +1.75D.

thanks.;)

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## Darryl Meister

Just multiply the distance of the segment center in centimeters by the addition power (that is, 0.4 * 1.75 = 0.7 prism diopters).

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## benice

thank u so very much.

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