"ascertain by exact measurements," mid-15c., from Anglo-French gauge (mid-14c.), from Old North French gauger "standardize, calibrate, measure" (Old French jaugier), from gauge "gauging rod," a word of unknown origin. Perhaps from Frankish *galgo "rod, pole for measuring" or another Germanic source (compare Old Norse gelgja "pole, perch," Old High German galgo; see gallows). Related: Gauged; gauging. The figurative use is from 1580s. "The spelling variants gauge and gage have existed since the first recorded uses in Middle English, though in American English gage is found exclusively in technical uses" [Barnhart].