@alidan no it isn't giving you ground of anything, is wrong knowledge and it won't give you any idea to understand the currency.
Also, your example doesn't apply because he isn't going to make an exchange of currency (and it dismisses money devaluation), he is going to earn local currency so it doesn't matter how many yens, dollars, pesos, etc was the value, because he is going to earn is the money of that place.
so that an apple cost 1 gold (or whatever) but was 10XX yen (or whatever) is meaningless info, it doesn't tell you if something is cheap or not. What will tell you if something is cheap is for example an apple cost 1 gold, and that potion cost 20 golds, but what I earn in a day is 10 golds. see? relevant information it tells you what is cheap and what isn't.
so japs going and going about that "equivalency" is utter bullshit.