How does report know which fields can be converted and how?

>I have a cursor that is used for the data source of a report. Just numbers. The report displays the numbers in metric or english depending on the users preference, but the data is actually held in the cursor in english.
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>I also allow the user to dump that data table out to an excel file, via the "export" function. My problem is; now I have someone wanting that data file in metric.
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>Since the structure of the cursor varies, depending on the choices, this is seeming like a tedious task. Any suggestions?