Coinage and currency
The basis for the currency system is a pound of silver of a standard purity broken up into 240 pennies. There are 20 pennies to a shilling (which obviously weigh a troy ounce). And 12 shillings to a pound. Different countries and reigns use or used silver of different purities, so the worth of coins is not strictly uniform.
Coinage of other metals exist, but these are commodities, not currency.