Ounces And Troy Ounces

Both are based on the grain.

avoirdupois is 437.5 grains to the oz, 7000 to the pound
troy is 480 grains to the oz, 5760 to the pound

So a pound of butter weighs about 21.5% more than a pound of gold.

A pennyweight (dwt) is 24 grains, or 1/20 oz
20 dwt = 480 grains or 1 oz
240 dwt = 5760 grains or 1 pound

240 silver pennies weigh one pound
240 pence (old system) are worth 1£
Thus, the "pound sterling" was originally a pound of sterling silver, and a penny was a pennyweight of silver.

A copper cent weighs 2 dwt.