How to convert old amounts into different currencies?

I want to calculate different amounts in Yen, Yuan, Euro and other currencies from 2007 to 2011 into dollars. Should I use historic rates and simply divide them? Or use a current rate? Given the different exchange rates at different times, will using historic rates be a better representation if I am using this for... show more I want to calculate different amounts in Yen, Yuan, Euro and other currencies from 2007 to 2011 into dollars. Should I use historic rates and simply divide them? Or use a current rate? Given the different exchange rates at different times, will using historic rates be a better representation if I am using this for research.
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