I do quite a bit of currency conversion, and the trick is to create an ID that can be tied to the conversion rate. for my particular use case, the ID is FromCurr&'-'&ToCurr&'-'ConversionDate (USD-CAD-03/22/2018) and the rate. I then use this as a mapping table into my app to normalize all currency into the desired rate. By having one mapping table, i have the bonus of being able to use the same applymap against multiple fields so that i can have multiple normalized rates. This way if my app needs to have USD, EUR, and CNY, then i have the flexibility to do all 3 without extra effort.