New sensors have a calibration period ~8-16+ hours and typically become more accurate as you wear them.
Why do I get a different reading from a finger prick glucometer vs my continuous glucose monitoring sensor?
Both finger prick glucometers and CGMs have some error margin. The gold standard for accuracy is a blood draw measurement and both finger sticks and CGMs have error margins (MARD) to that standard. Finger sticks tend to be in the range of 5-10% MARD, while the Libre has a MARD of about 9.4% over 14 days.
Additionally, CGM measures your interstitial fluid, which has a 10-15 minute phase-shifted delay vs a finger prick blood reading. When you are on a rise or a fall in glucose levels (as opposed to flat and steady), the difference between finger prick glucometer and CGM measurements will be more pronounced. You should only compare readings in a fasted state.
Where can I get more information on sensor accuracy?
You can read more information from the device manufacturer here: