system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How did currency exchange rates form in the very beginning?

I was wondering how exchange rates formed in the beginning. As in, when the first two countries came together to exchange a monetary deal, how did they know how much of their money equated to the other countries money.
gpt
Countries often initially had their currencies locked to a precious metal (typically gold or silver). For example pound sterling (GBP) derives its name from when 20 shillings was literally a pound of sterling silver, under Anglo-saxon rule. These are pretty easily exchangeable because the international value of that coin is its metal content.