Regarding non-metric mass. More proof of the superiority of the metric system.

Metric

A gram was initially standardized as 1 cm3 of water at 101.325 KPa = 1 atm, and its densest temperature (ca. 4 C).

Avoirdupois

The avoirdupois weight system is used by the USS (U.S. System) and the British IS (Imperial System). The word avoirdupois is derived from the Old French for "goods of weight" (as opposed to goods sold by the piece). The avoirdupois is the default or international pound.

The original avoirdupois had these units and are used by the USS.

The IS was modified around the "stone" unit:

Troy and Apothecary

The troy weight system is used for precious metals and gems. It is named after Troyes, France, an important city of trade during the Middle Ages. It is independent of other systems of measurement such as metric (SI), American (USS), or British (IS).

Note that a troy ounce > avoirdupois ounce, but a troy pound < avoirdupois pound.

The apothecaries' mass system was used by pharmacists and chemists. The apothecaries' system has the same troy pound and troy ounces but then subdivides differently.

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