As a reminder, glucometers available on the market are supposed to be within 20% of a serum lab glucose taken at the same time as a finger stick. As glucose levels rise, the margin grows.
All CGM devices, whether it’s a Freestyle Libre or any of the Dexcom models, are measuring interstitial glucose (that the fluid between your body cells), and will be slightly different. If you’re getting readings on your CGM that are trending up or down quickly, it’s likely to be further off from a finger stick.
All that said, my son’s Dexcom G6 has been accurate to within 10 mg/dL on the occasions when I’ve had him check, and as such, we don’t worry about doing finger stick checks unless he’s having symptoms that don’t seem consistent with his readings, and it works seamlessly with his tSlim x2 pump.
As always with T1D, it never hurts to check, just be careful about chasing your tail. It takes about 40 minutes to see changes in his CGM trend after dosing or eating.