Thanks I didn't know about the cal factor but it sounds right. I used the 530g for 3+ years and am now using the 630g. So by just experimenting, I found a few tricks. I put in a new sensor first and turn off the sensor function of the pump. I mark the time and after the two hours (the timer is in the transmitter - independent from the pump) I check my bg. If it's not too high or low and not rising or falling much, I turn on the sensor function and tell it to find the new sensor. In a minute or so, the pump wants me to calibrate my sensor.
If my bg is fairly stable, I calibrate again in 2 or 3 hours. I generally calibrate at least one more time the first day. The accuracy isn't at its peak yet, but it gives me a good idea of where I'm at.