The most useful economic measure for the traveler in this situation would be the exchange rate.
It is the expression of the relationship between the price of a country's currency in relation to the currency of another country, in order to quantitatively express the exchange condition between the two.
Therefore, in this situation, it would be ideal for the Japanese traveler to plan ahead for a foreign trip and exchange his currency for the currency of the country he will be visiting.
Find out more about exchange rate here:
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