Start with the evidence
Record the rate source, date and intended use alongside its value. Keep these separate from the document date if they are not the same.
Work through the example
A working sheet uses a fictional rate labelled 8 October, while its note says 9 October. Even if the numeric result looks reasonable, the mismatch needs clarification before the calculation is relied on.
Make the next step clear
Ask the responsible reviewer which source and date are appropriate. Preserve the original information and document any correction rather than selecting a date just because it produces a convenient total.
Keep the source context
All exchange rates in these worked examples are fictional arithmetic inputs, not current market rates. A business must use the source, date and method appropriate to its own review and approved accounting process. Keep original currency amounts available throughout.