The concept of convenient numbers is related to that of preferred numbers. A structure is defined to build a set of numbers that are convenient for use by humans in counting or measuring. National Bureau of Standards (NBS) (which was later renamed to the National Institute of Standards and Technology (NIST)) defined a set of convenient numbers during the 1970s when it was developing procedures for metrication in the United States. The NBS technical note describes that system of convenient metric values as the 1-2-5 series in reverse, with assigned preferences for those numbers which are multiples of 5, 2, and 1 (plus their powers of 10), excluding linear dimensions above 100 mm (because such measurements are defined by another set of rules), from which the Schedule of Convenient Numbers Be