I have a caliper, it's more procedural ... when you undo the bar clamp bolt, the end expands, to let the bar out.. so in theory the measured diameter without the bars in will be larger than the true clamping diameter. So if I tighten the clamp bolt to get the actual diameter, I have no idea how far the clamp will close when the bars are in, so its guesswork if its the right diameter. Or am I being far too anal, as there are not enough diameter variations in vars ti make it worth my time?