After considerable research, I've tried to categorize the origin of all the non-SI units I can find that are CURRENTLY USED IN THE UNITED STATES--some 265 of them. This is a difficult task, because many units have multiple or obscure origins, I can't always be sure if a unit is really still in use, and I undoubtedly missed some specialized units. But here is my tentative breakdown: 28 % INVENTED IN THE UNITED STATES (non-metric, including business, industry, science, and military units). 20 % METRIC (non-SI, including metric-English hybrids, regardless of country of origin). 19 % WORLD CUSTOMARY & SCIENTIFIC (neither metric nor English; includes many ancient time and angle units and astronomical units). 19 % BRITISH/U.S. INDUSTRIAL & SCIENTIFIC (invented since the industrial revolution; some may have been invented in the U.S. but I am unable to verify which ones). 13 % MEDIEVAL ENGLISH VERSIONS OF OLD EUROPEAN UNITS (origin Greek, Roman, French, Italian, Germanic, etc.) 2 % INVENTED IN MEDIEVAL ENGLAND (no precedent in other countries) As this breakdown shows, we can't fairly describe our chaotic collection as "English", "customary," "colonial," "inch-pound", or any of the numerous other ad-hoc terms people have come up with. Over the last half-century or so, the number of non-SI units in use here and elsewhere has dropped dramatically (by many hundreds) as cumbersome old units have died out or been replaced by metric, and as obsolete metric units have given way to SI. However, some new non-SI units have been recently introduced (such as the abominable "Dobson unit"). NOTES To provide a fair comparison to the thirty SI units, I EXCLUDED: (1) extinct units such as the scruple, dry gallon, troy pound, and gill, although they may still be on the law books. (2) numerous compound units without special names or unique abbreviations (such as Cal/d, ft/s2) (3) numerous prefixed multiples, such as milligal and kilobar, UNLESS prefixes are normally not used with that unit (e.g., microinch and kilopoundforce (kip), which I did include in the list). (4) units such as the gon [grad] which never seem to have been used here, although they may appear in foreign sources. I INCLUDED: (1) compound units with special names or abbreviations (e.g., psi, cfs, gpm) (2) old units no longer in widespread use but still common in some fields (e.g., hand, furlong, grain). (3) "gauges" used as units, even if the increment is not consistent (e.g., AWG, USS ga) (4) non-linear measurements used as units (e.g., Richter magnitude, stellar magnitude) I welcome all criticisms. If anyone is interested, I will send them an Excel attachment with the complete table. (I don't attach unsolicited things to my postings.)
