Currency pair quoting order, also called the quotation convention, decides which currency is written first in a pair and therefore which one you buy or sell when you open a position. The market follows an informal seniority ranking: EUR comes first, then GBP, AUD, NZD, USD, CAD, CHF and finally JPY. That is why prices are quoted as EUR/USD rather than USD/EUR, and USD/JPY rather than JPY/USD.
The first currency is the base, the second is the quote, and the price shows how many units of the quote currency one unit of the base is worth. The order matters because it fixes the direction of a trade and the way pip value is calculated.
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How to Check the Way a Currency Is Managed
The regime behind a currency is published, not inferred. The four primary sources that say how a rate is governed, what each one can and cannot tell you, and how to keep the answer from going stale.