The convenient numbers in this article were developed in the US in connection with the attempted introduction of the metric system in the United States in the 1970s.
An 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).
For example, where a tape or a scale is graduated in intervals of 5, any value that represents a multiple of 5 is more "convenient" to measure or verify than one which is not.
In addition, where operations involve the subdivision of quantities into two or more equal parts, any number that is highly divisible has an explicit advantage."
n × 50 n × 20 n × 10 n × 5 n × 2 n × 1 Notes: The Technical Note also states, "In the practical application of a "convenient numbers approach" to the selection of suitable metric values, it is desirable to start with the highest possible preference and then to gradually refine the difference until an acceptable and convenient metric value has been found."