Troy Pound (lb t)

The precious metal pound of twelve troy ounces, or 5,760 grains, and the standard by which English coin was struck after Henry VIII abandoned the Tower pound in 1526.

Twelve ounces make a troy pound where sixteen make an ordinary one, so the troy pound is the lighter of the two despite being built from heavier ounces. That single inversion has confused people for six centuries and is the whole mechanism of the pound-of-gold-against-a-pound-of-feathers riddle. Henry VIII adopted it in place of the older Tower pound of 5,400 grains, a change worth noticing in a reign otherwise notorious for debasing the coinage: a heavier nominal pound of silver yielded more coin, and the Crown kept the difference. The troy pound was abolished for British trade by the Weights and Measures Act of 1878, which spared only the troy ounce.