Find a Scope's Optical Zero

A scope badly off optical zero Hold the objective end close to a mirror under a good light. I used my bathroom mirror. You'll need to tweek the scope/mirror distance and your eyeball/occular lens distance. Tweek distances until you see two crosshair images, one dark and centered and one lighter and not centered.

The gif image on the right shows how one of my pistol scopes looked through a mirror. The scope was adjusted way high and way to the left. To return the scope to optical zero, I simply adjusted the knobs until the off center crosshair aligned with the center, darker crosshair.

Don't ask me how it works 'cause I don't know. I just know it works and works fast and easy. It works with fixed, variable, and even pistol/LER scopes.