Grain

There are 435.5 grains to an ounce.

POINT FIVE?  Sheesh.  Why a half grain?  Now I gots to know.

The two were units linked.  32 grains makes a silver penny, and 20 pennies makes and ounce.  640 to an ounce.  But that's 1200 years ago, and the two plainly shifted in intervening centuries...

Ah, in 1824 and 1855, one pound was set to 7000 grains.  And a 16th of 7000 is....    435 and a half.  After 1855 metric starts to infect proper management as it crosses the channel like a panicky Wuhan resident fleeing his home country for Western medicine.