For most users, chrono calibration in the normal sense is impossible. About the only way it can be done is to use a laboratory certified chronograph for comparison, and how are you going to do that? As earlier stated, using a factory load having a published velocity is a waste of time, as whatever test gun that Remington, Winchester, etc. used to get their velocity is not your gun. As stated, the most valuable information you can get from your chrono is a general idea of velocity, the change in velocity with different bullet weights and types, and different propellant charges, and the standard deviation of the MV of your ammunition.

With some basis in statistical theory and also from personal experimentation, the average velocity and SD obtained from firing 5 shots provides about as good data as anyone needs. More than that just wastes ammunition, but if you feel 10 or 20 shots is a better sample size, have at it.