First day of sensor use is typically less reliable, that's not a problem. But in this case it is wildly off base, checked him at 2a and it said 60..he was 92. Checked at 5a and it said 300! I was all worried about a rebound so I downloaded to look at the trend and asked him to verify with meter. He was 120. Calibrated on both readings (mostly to show the endo as we have an appt this week, didn't want them think he was going from 60 to 300 in a few hours!). When we've had sensor issues it just won't work, shows ?? or whatever, our main issues in the beginning were adhesive issues, and it just came off. I'm curious when you decide to yank, do you give it a day or how long?