I agree. First every process has variation so even though the goal is to have the same measurement from bank to bank and cylinder to cylinder, there is a tolerance or variance that you will see in this number. Next, your measurement is a process as well and that is highly prone to variation so it's quite likely that if you're getting (for example) a .005" difference between cylinders, .003" might be the actual height variation and .002" is a variation "adder" based on your measurement method, measurement tool and the human interaction with both the method and tool.

- EM