The “minimum acceptable accuracy” of SMBG devices according to ISO standard used for meters is 95% of the readings over 75 must be +/- 20 percent. At readings under 75, 95% must be +/- 15 mg/dl.
The FDA does not require meter manufacturers to abide by the ISO standard, but most chose to.
If you can find the owner manual for a meter online, you should be able to see the “performance characteristics” table with the results of testing for accuracy and precision. This, of course, takes some effort.
For people who are really sensitive to insulin and for children who have rapid changes in blood glucose levels, meter accuracy may be of great concern.
Personally, as a long-time type 1 who tests frequently, I don’t get too worked up over meter accuracy. Even if a reading is off by 20 percent or 15 mg/dl, it wouldn’t really change my immediate treatment efforts (I treat anything under 70 with glucose tablets, 1 tablet = 15-20 points for me. As long as I wait the recommended 15 minutes and test again, I’ll know if the glucose I took was adequate).
For highs, I treat with correction units of insulin. True, a number that is 20% off could cause me to take not quite enough of a correction dose, or perhaps a bit too much. But if I’m high already, the worse that could happen is I’m a bit high before my next meal or the number drops a bit more than I calculated (but since I was high, probably not low enough to send me into a hypo).
Yes, I would appreciate more precise and accurate meters–but I don’t at all want to pay more for the devices or the strips!