Lensometry
Neutralizing spectacle prescriptions — sphere, cylinder, axis, add, and prism on the lensometer.
Reading Glasses Like an Instrument
What it reads — back vertex power: sphere, cylinder, and axis, plus prism and the add of a multifocal. Neutralize the distance portion through the back of the lens, geometric center first.
Technique — focus the eyepiece on the reticle before anything else (or every reading inherits your own refractive error), center the mires, and turn the power drum until the sphere lines clear; rotate and refocus for the cylinder lines. One clear reading for both line sets = a sphere.
Prism — a mire cross displaced from the reticle center; the rings count prism diopters and the displacement direction gives the base.
Reading the add — neutralize distance, then the segment; the difference in sphere power is the add. Progressive lenses use the marked fitting reference points.