The Glucose Management Indicator on my Freestyle Libre 3 usually runs slightly lower than my actual A1c. But it's close enough, and I don't mind mentally adding a half percentage point in order to "calibrate" it. Day-to-day readings can vary a few points up or down, but so can various meters vary with each other. I can easily check how close my CGM reading is with my BG meter by doing a quick fingerstick test. My Libre been a tremendous help to me over many years, now. I consider it essential for dosing insulin, and only pay a little over $80 out-of-pocket for two 14-day sensors every 28 days at Walgreens.