Finally a man who understand how to explain a world economy to a reader.
" I sell you this."
"You give me X coins."
"For A coins I can eat." "and for B coins I can sleep in a inn."
He establish the basic living expense (eating/sleeping) so we know how this world works.
Only after doing this that you can convert the currency into yen.
Thank you, only for this I'll rate it 10/10.