Making it readable

Four habits do nearly all the work. Label every row and column in words a stranger would understand. Keep one sheet for raw data and another for the calculation, never mixed. State the units and the date at the top. And add a short note saying what question the sheet answers — a sentence that costs a minute and saves whoever opens it half an hour.

Finally, mark anything estimated as an estimate. A sheet that quietly mixes measured figures with guesses is the one that gets acted on wrongly, and the person who notices is rarely the person who built it. Marking your own uncertainty is not weakness in this work; it is the part that makes the rest of it credible.