why is the representative fraction (rf) the universal standard for scale
Scale (map) Actual printed maps are produced from the projection map by a constant scaling denoted by a ratio such as 1:100M (for whole world maps) or 1:10000 (for such as town plans). To avoid confusion in the use of the word 'scale' this constant scale fraction is called the representative fraction (RF) of the printed map and it is to be identified with the ratio printed on the map. The actual printed map coordinates for the equirectangular cylindrical projection are
Metrication in the United States Although customary units are used more often than metric units in the U.S., the SI system is used extensively in some fields such as science, medicine, the military, automobile production and repair, and international affairs. Post 1994 federal law also mandates most packaged consumer goods be labeled in both customary and metric units.[4] Still, most Americans are unable to make metric conversions,[5] but smartphone apps can help (e.g. on iOS[6] and Android[7]).