Powder testing is done by using "powder-type" spray deodorant or foot spray to tell if you're getting contact with the rest, shelf, riser, etc. Just spray it on the latter 1/3 of your arrow and your vanes. Shoot into something that is not going to let the vanes go through, then look for signs that the vanes are making contact with something on your bow. (Sorry if I'm not very good at explaining clearly) There should be small marks where your arrow rides the rest, but nothing else if you're getting adequate clearance.