I bought my wheeler torque wrench, same as above, for scope rings and it's proven to be useful for all sorts of other things too - most recently, setting critical marine hose clamps just right. It's a great tool.
A scope leveling kit/tool is real helpful installing a scope also. And possibly a scope level isn't a bad idea for 400 yard shooting either...
You basically get the rifle square to gravity on a rest via the tools. Then you hang a plum bob about 50 yards away, set the scope hairs to the plum bob, then through iteration of small adjustments and checks you got a scope torqued straight to the rifle. Things get knocked a little off, best to have an hour, relax, get it just right - no need to rush, it's fun..
Then if you got one, last step you use the plumb bob finally to square your mounted level...
There are various ways to do this - you can even set the scope level first (since after all, it's based on the cross hairs and gravity - your plum bob).
Then, when shooting longer distances, you have a reference to know if you are level (adjustments, if the rifle isn't quite level, aren't going to be quite right, either).
I use purple loctite on scope mounts and rings. Sucks when they get loose, actually can damage things if you don't notice.
Tool:
Amazon.com
Scope level (this happens to be an Arken), they are matched to your tube size btw: