As my annual Hba1c gets closer, I start to use Mysugr app. I know it isn't that accurate, but it gives me some idea of what my blood test may deliver. The actual blood test looks over a 2 -3 month timescale and also checks other stuff that the app doesn't do. I normally add 3 to the estimate and see how close it is. I do the same thing every year, I surely can't be the only one?