Glasses VS. Contacts. Not the same number.

When contacts and glasses round to different numbers

The bending is the same on both planes; the distance from the cornea changes how much bending is needed. Below −3.50 D the math rounds the contact and the glasses to the same 0.25 D step — no difference printed. Above it, the gap survives the rounding.

Formula: F_contact = F_glass ÷ (1 − d × F_glass), where dis vertex distance in meters. Cylinder usually carries across unchanged unless you're above ~−3.00 cyl.