When mounting a riflescope, it's a good idea to use a level to ensure that the horizontal crosshair lies perfectly flat and the vertical one isn't canted in relation to the gun. If you don't have a level handy, just bust out your iPhone. Select the compass app, swipe left—and now you have a level. The ideal scope-leveling scenario involves a long, one-piece scope base or a Picatinny rail, either of which allows you to level the rifle and the scope more or less simultaneously. But a lot of hunting-rifle setups are like the one in the video, with no rail and two-piece bases/rings. In this case, you can use a gun vise and level the rifle off the flats on the bottom half of the rings (especially if you first use the phone level to make sure the bottom rings are perfectly square). Then tighten the vice, position the scope, and level it by placing the phone on the top turret with the scope cap removed. As long as both the gun and the scope read level, the crosshairs should be perfect. The video shows exactly how to do it.