The riser.

Take a 3' level hold it against the sides on both the top and bottom limb pockets match the sight bubble with the level bubble and your set.

I would say even if your level on your sight isn't perfect its not going to matter to much as long as you hold it the same every time!

If it's off severly you will notice that at longer yardages your arrowws will all hit either to the right or left depending withch way your sight level is off!