Comparing finger pricks and CGM's is not really directly comparable, as one takes a one-time measurement from blood whereas the other measures continuously from interstitial fluid. CGM's are meant to track trends and see your overall condition with glucose, whereas blood tests give you a snapshot of a given moment. As the CGM measures from interstitial fluid, there is also a slight delay compared to the blood measurement.
When you test your glucose using a glucometer, you measure the glucose directly in your blood. However, the Freestyle Libre sensor we at Veri use measures glucose in the interstitial fluid, rather than in the blood. There’s typically a delay (5-15 minutes between the glucose levels in the blood and the interstitial fluid). Like any data, your blood sugar data is not always 100% accurate. The accuracy comes from of course the sensor, but also from the software algorithms used with it.
The manufacturer of the sensor (Abbott) focuses on fine-tuning the very low and high ranges, as they are trying to be super accurate for the dangerous ranges for diabetic users. We, however, focus the accuracy more on the middle ranges, where non-diabetics tend to be. We therefore use a slightly different algorithm from them, and this will sometimes have varying results. An average 10 mg/dL difference between different measurement devices and apps is fairly common since the sensor accuracy for both parties is often +- 20 mg/dL - we are still working on improving this as much as possible! The most important thing about glucose monitoring (if not for medical use) is the trends of your blood sugar - stability, spikes, and fluctuations.