Help, question; how to "optically zero" a used scope...???

Mirror method-place objective on mirror and look through scope. Adjust until only one reticle is seen. Not experienced with this method myself but many swear by it. There are preferred settings for magnification and parallax to do this but I'm not sure what is recommened. I'm sure others will post such or you can search for the information.

Count clicks-rotate turrets fully to one extreme then rotate to the other limit counting the clicks. Set at half that number. This method sets scope at mechanical center but is it optical center? Probably close enough for any real use but I'm not certain.

Two ways I know of, set scope in v block, look through scope and make spot on wall where cross hair is, rotate scope in block 180°, move with scope adjustment half way to spot on wall, repeat as needed. Place scope on mirror, if lighted turn on move two cross hairs together with scopes adjustment s, if not shine light in scope next to your eye, move two cross hairs together.

https://www.youtube.com/watch?v=SvgOKMX9Gvg