The more popular air rifle in the world is the BSA Meteor. Firing either .177 or .22 calibre pellets, the Mk 6 and Mk7 Meteors is the standard for serious air-powered guns. They have a maximum hunting range of 55 yards and a maximum target range of 70 yards, but because they are meant for shooting small-game targets, scopes are actually quite useful for these rifles.
Get a medium-sized cardboard box an cut the flaps off.
Cut two V-shaped notches into the box, on the top edges of the sides, so that the scope can be placed on it.
Put the box in a place with a view, and then place something heavy, like a brick, in the bottom of the box, so it will be stable.
Pick something to view, and watch it through the scope as you rotate the tube around 360 degrees to see if the reticle stays in the same place, or if it moves.
Adjust the turrets if the image is moving, and do so until the reticle is fixed in place.