Modern metrology takes no account of money. In practice, coin was tied to
bullion for a great part of history, this ended in the various Brenton Woods
agreements after the world war.
In practice, coin was either wieght of bullion (eg pound), or notionally
thus. Pre-decimal money often occured with weights and measures (being one of
the weights, usually).
Britian used the money of Charles the great, being 1l of 20s. of 12d.
this being fairly easy to reckon on the abacus. Other countries used things like a
florin of 60 kreutzer, or a rixdollar of 30 groshen of 12 pfennigs.
Often minted coin of other countries were traded either at value or declared
rate.
Currency decimalisation usually preceeds decimalisation of the units. By 1800
only Russia and the US had a unit divided into 100 smaller ones. The main unit
still varies in name, but the lesser name of cent and mill are often seen.