Optical zero?

So I've been aware for a while of the technique of tin foil over scope lens with a small hole, set zoom lowest,ao lowest,get target as close as possible within foucus and fire a shot then measure from bulls to shot for scope height.
Supposed to give more accurate measurements in chair gun.
So finally going to try it.
The one thing i cant find on any video is wether I need to be set to optical zero, or if i can do it sighted in.
Can anyone help me on this please.
Cheers

Hi Pete.
Yep but Im trying this way to see if it's more accurate than the half scope height and center of bore.

This is in the above which I thought was interesting.