Ok, you don't want to try from underneath! You can easily locate the hole that you want to use from underneath, and transfer your measurements to the top. Cover the top area w/ blue tape so you can make marks. All of the holes should be on an even number measurement, MOST are 4" center to center. So locate the center of the faucet hole from underneath, by using the very back of the circle, that's the center. Now measure to the center of the hole you want to use. I would guess it will be 8" or 12". With that measurement, go up top and find the center of your faucet at the back of it, and measure to the center of where you want the new hole. So now you have the side to side located. The front to back is simply the same distance from the wall as the center of the faucet, 90 degrees from where the center is on the back. The quartz is NOT friendly on ANY drill bit! I believe HD has a diamond tipped line that I made work, but you might need 2. Go at least 1 size larger than the minimum, the flange will give you plenty of wiggle room. Source: am countertop guy, that builds as a hobby.