It may also be interesting to note that the dollar, the German mark, and the British pound are actually units of weight, primarily used for silver. However, the heller and the pfennig were much smaller units of weight in the Middle Ages, equivalent to approximately 1 g or 1/2 g of silver. Mint masters could regularly “declare” old coins invalid. The population was required to exchange them for new coins. Melting them down was prohibited under penalty of death.
Example: For 10 old pfennigs, people received only 9 new ones. The difference of 1 pfennig was the seigniorage, or revenue for the mint master.
In practice, this functioned like a recurring tax on cash holdings.
Ironically, this tax concept could also be implemented with Bitcoin—but not with Monero. Monero effectively “melts” the coins, making them fungible, so that 1 XMR = 1 XMR.