Hey Jerry, I usually lay out the carpet and then take a poker, like a toad stabber, to locate the hole edges, then a sharp knife into the hole and cut a perfect circle, using the hole as a guide. Helps to find screw holes as well. Larger holes, I try to leave that to precise measurements from key components, or if, like a shifter hole, you can get a rough location to start and then pull the carpet over and continue to trim away a little at a time until it is all the way down.