CGMS calibration question

I am on day 11 of CGMS (MM 722 pump) – getting data that is pretty interesting and is going to be a help. One aspect I am trying to get better with is the calibration and stability. How long is long enough for "stable" BG to get an accurate claibration. My instructor told me not to look at the 3 hr graph, but to use the 24 hr to gauge stablity. All you folks on CGMS – how long of a stable period do you look for before you will use a finger stick to calibrate?

Thanks for your help.

Ken