You are making it way more difficult than it really is. If you set the dial to zero going in, every reading you get is a direct reading on the dial. In other words, if the dial reads 23, the measurement is .623 or .723. If the muzzle reading is 97, the muzzle diameter is .697. The whole idea is to move the settings of a measuring device as seldom as possible and to have as much direct reading as possible. My Galazan micrometer reads 16 gauge just fine. The only exception is that it will not read an extremely full choke. If the gauge stops in the barrel, you know you have more choke than the reading on the gauge when the gauge stops. No fuss, no muss. What is the difference between .026 and .034 in a 16 gauge choke? They're both full. When I see someone resetting a gauge when it is in the barrel of my gun, I take the gun away from him because I know he doesn't know what he is doing and is not going to buy the gun.
