How to calculate the error of blood glucose meter

Compared with hospitals, they are mainly confident (for example, the hospital test is 6.5, the blood glucose meter is 7, and the blood glucose meter is about 8% higher). It doesn't matter whether the blood glucose meter test paper is higher or lower than that of the hospital, except that it is ridiculously high or low. The main thing is that the same batch of test paper should be stable, not today.