Start with the evidence
Write the rate as units received per one unit of the source currency. Check that the operation you plan to use matches that wording.
Work through the example
At a fictional USD1.20 per EUR rate, EUR50 multiplied by 1.20 gives USD60. Dividing by 1.20 instead would answer a different conversion question and produce the wrong result for these inputs.
Make the next step clear
Keep the written rate direction beside the formula in the review note. If a source presents the inverse rate, clarify it before comparing or calculating amounts.
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.