I had occasion to read the ISO 15197:2013 standard about blood glucose meters Section 6.3.3 “minimum system accuracy performance criteria.”
Note that this accuracy requirement is what is typically cited as the accuracy requirement for glucose meters.
But the two Notes in this section say that testing meters with actual users is tested elsewhere in the document (section 8). Thus, because of the protocol used, the system accuracy estimate does not account for all errors since user errors are excluded. Hence, the system accuracy requirement is not the total error of the meter but rather a subset of total error.
Moreover, in the user test section, the acceptance goals are different from the system accuracy section!
Ok, I get it. The authors of the standard want to separate two major error sources: error from the instrument and reagents (the system error) and errors caused by users.
But there is no attempt to reconcile the two estimates. And if one considers the user test as a total error test, which is reasonable (e.g., it includes system accuracy and user error), then the percentage of results that must meet goals is 95%. The 99% requirement went poof.