The biggest problem with variance in a blood sugar reading is when people are dosing insulin based on that reading. And 15 to 20 percent of a blood sugar level at 100 mg/dL (according to your meter) means your blood sugar level may actually be at 120 mg/dL or 80 mg/dL...
You might be wondering why the FDA doesn’t tighten their standards. Unfortunately, there are a variety of factors that account for that acceptable variance range...