Canadian dollar
Because Canada's primary foreign-trade relationship is with the United States, Canadian consumers, economists, and many businesses primarily define and value the Canadian dollar in terms of the United States dollar. Thus, by observing how the Canadian dollar floats in terms of the US dollar, foreign-exchange economists can indirectly observe internal behaviours and patterns in the US economy that could not be seen by direct observation. Also, because it is considered a petrodollar, the Canadian dollar has only fully evolved into a global reserve currency since the 1970s, when it was floated against all other world currencies.