When not otherwise provided by law, the director may inspect, and test to ascertain if they are correct, all weights and measures kept, offered or exposed for sale. He shall inspect, and test to ascertain if they are correct, all weights and measures commercially used in (1) determining the weight, measurement or count of commodities or things sold or offered or exposed for sale on the basis of weight or of measure or count, (2) computing the basic charge or payment for services rendered on the basis of weight or of measure or count. With respect to devices designed to be used commercially only once and to be then discarded, and with respect to devices uniformly mass-produced as by means of a mold or die and not susceptible of individual adjustment, the inspection and testing of each individual device shall not be required and the inspecting and testing requirements of this section shall be satisfied when inspections and tests are made on representative samples of such devices; and the lots, of which such samples are representative, shall be held to be correct or incorrect upon the basis of the results of the inspection and tests on such samples.