Chairgun scope height.
Mark a cross on something like a Yellow pages.
Set your scope to minimum PA adjustment.
Cover the Objective lens with tinfoil and poke a small hole (3mm) in the centre of the foil.
Sight the cross on the yellow pages and with your muzzle as close as possible to the yellow pages fire a pellet.
You can now measure from the centre of your pellet hole to the cross you've marked.
This will give you your scope height for Chairgun.
Originally posted by Harry's Lad, the author of Chairgun.
Hope this helps.