Handbook 44 from NIST spells out rules and regulations for the weighing industry and separates weighing devices into five accuracy classes. Depending on the number and value of scale divisions, equipment can be either class I, II, III, IIIL, or IIII, with Class I having the highest precision. All Legal-for-Trade scales fall under one of these five classes.
Table 7a of Handbook 44 breaks down the description of each class. Class III states: “All commercial weighing not otherwise specified, grain test scales, retail precious metals and semi-precious gem weighing, animal scales, postal scales, vehicle on-board weighing systems with a capacity less than or equal to 30,000 lb, and scales used to determine laundry charges.”
What it’s saying basically is anything that doesn’t fall elsewhere would go here, providing the device meets the criteria for the quantity and size of divisions. Class III covers many different types of scales. It’s a bit of a catch-all. Produce scales would be one type of Class III application. While some jewelry scales are Class III if the resolution is appropriate for the application, a more precise jewelry scale could be Class II. It all depends on the number of divisions and capacity. Precision laboratory devices usually fall under Class I. At the opposite end of the spectrum is Class IIIL which covers heavier capacity on-board applications, truck scales, livestock scales and railroad scales. Class IIII applies strictly to axle scales and wheel loader devices for highway weight enforcement.