I use that but differently than recommended. I place the bar in a rail cut-out, and then with the rifle on a bipod or other rest, make sure the rifle is canted to be level. Then I align my vertical crosshair with something I know to be level. When I am in Phoenix, I use a 20 story building far off in the distance. I know the sides are plumb because when I bracket the top of building (which is flat) with my horizontal wire, the vertical fits perfectly along side the vertical side of the building. In the past I used my pool fence as a plumb line (verified with a level and square) but I prefer the building alignment now.
Once I have the scope rotated correctly, I place a level on the top turret as a second verification, then carefully tighten the screws. When everything is tight, I verify the level on the rail is level, my building bracket is square, and the level on the turret is level. I often have to repeat because the scope often slips just a bit while tightening.
https://www.americanhunter.org/cont...oop,rings, you are ready to adjust the scope.