Optic measurement

[SKami]

I see in some Ballistics programs that one element that can be entered is the height above barrel. I think this measurement is from the center of the bore to the center of your optic. Is there an accurate way to do this besides just using a tape. Does it matter?

I think it does matter for a number of reasons, one is available scope adjustment, and two is the angle of the bore center relative to true horizontal. This subject interests me greatly so I will tag along, but it seems to have spawned a whole industry based on POI changes relative to angle of shot-i.e. the newest range finders that take that angle in to account.