some of us find that our body has a responds to a foreign object being fired into it and it can take a day or two for this reaction to settle down. Foe this reason some of us, apply the sensor a day or two before we activate it, to give that reaction time to settle down.
Also Libre is factory calibrated to be most reliable in range but can over estimate above and under estimate below range, so if you are double checking a high reading above 10 then the sensor may be further adrift from BG than when in range. Likewise if levels are rising or falling significantly Libre will often over egg that rise and similar with a sharp drop.
I tend to double check my sensor with a finger prick when my levels are steady for about 30 mins in the 5s or 6s with no food or insulin active. Usually I will find it is within 0.5mmols of my BG meter in those circumstances and for me that means it is easily reliable enough to calculate doses from, but even 2 mmols is workable as long as it is reasonably consistent ie always 2mmols above or below BG reading. If it is more than 2mmols out for 3 double checks then it gets reported to Abbott and they will usually replace it.
It is important to ensure that you are well hydrated as dehydration will often cause it to give a higher reading as blood takes water from the interstitial fluid and that means that the glucose concentration of the interstitial fluid becomes higher.
I was out all of yesterday afternoon and didn't have a drink with me and when I got home I was developing a bit of a headache and my Libre reading was 8. I had a large glass of water it dropped to 5.9 in a bout half an hour as a result of rehydrating,
Hopefully your sensor will settle down soon and you will learn to identify and interpret some of it's little quirks and foibles.
We have a thread about the limitations and quirks of CGMs which I will link below. It is useful to give you more insight into when to trust it and when to double check.
Moderator Note: This helpful reply was copied from another thread as it details some of the commonly experienced limitations of continuous glucose sensors.
My blood sugar has been in perfect range for days now, but although I haven't changed anything, I'm starting to get very short periods of hypos while I sleep and this morning I had a hypo alarm.
If these are very short periods of lows and occur overnight, they are more likely to be compression lows - when pressure is applied to a sensor, it will report a false low. The reason I say this is more likely to happen at...