Write the source value with its unit, choose the target unit, and check whether the context requires an exact or rounded result. Converting 5 feet to meters is different from converting 5 square feet to square meters; a missing exponent changes the answer.
Use the unit converter for a first pass, then convert back or compare with an independent reference for an important value. Round only at the end and state the precision used. For rates, include the time basis and, where the rate can change, the timestamp.
A plausibility check can catch an order-of-magnitude error before it reaches a form or report.
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