Mass. Gen. Laws ch. 98, § 33A

The deputy director or his inspectors, under his direction, shall at least once in each year test all weighing and measuring devices which are used for the purpose of buying or selling goods, wares or merchandise, for public weighing or for hire or reward, in towns of five thousand or less inhabitants, and shall mark them in accordance with the results of such tests. The number of inhabitants shall mean the population as determined by the last preceding federal census.