Have I created enough space for the restorative material that is planned? One way to test that is to take a well fitting copyplast, line it with a limited amount of bite registration paste and seat it firmly against the tissue. Once set, it can be peeled out of the copyplast and measured. The first photo shows the copyplast seated in a putty matrix with bite registration in it, in the second you see the bite registration paste removed and being measured. If the planned restoration for that second molar being measured is cast gold I might be okay at .8mm; if it’s Zirconia I’m probably a little shy; if it’s lithium disilicate (E-max) I’m well outside manufacturer’s recommendations (1.5mm at the thinnest part). Time and again I discover that despite my use of guides as I prepare teeth, I often discover areas that need to be altered as I use multiple methods to check my reduction. The redundancy of multiple checks ensures that the lab gets what they need - so I can get what I need - and my patients can get what they want.