@superball@SRLevine Avoirdupois ounces - US weight (and Imperial I think)
Troy ounces - fuck you ounces used by gold traders for fancy gold reasons
Metric ounce - STOP IT NO WHY (varied by country usually around 30g, see also the "metric inch")
Water ounces or Fluid ounces, US - measure of VOLUME, and smaller than:
Water ounces or Fluid ounces, UK - measure of VOLUME, also
and that list is NOT complete. those are just ones still in use in the last century.