A method is presented for determining whether a sufficient proportion of a product meets specifications when the available data are subject to reading error. The method is illustrated by an application in which a producer is required to verify that at least 95 percent of the containers of a product provide the net weight indicated on the container label. In this example, errors in reading the filled container weights and random variation in the empty container weights might at first lead one to conclude incorrectly that the proportion of containers that meet the requirement is insufficient.