Greg, I don't bother with setting the gauge to 0 when it is in the barrel, just subtract the muzzle measurement from the bore measurement to get the choke constriction. With the measurements you have bore is .725, muzzle is .696, choke is .029. David's method is handy when you are trying to find the beginning of the choke.

Jim

I learn something every day, and a lot of times it's that what I learned the day before was wrong