Spreadsheets are flexible, which makes structure especially important. When quantities, formulas, assumptions and presentation are mixed together, a small revision can become difficult to trace.
Give each column a job
Use clearly labelled input columns for quantities and resource rates. Show the unit beside the quantity. Keep calculated unit rates and totals distinct from editable inputs.
That separation helps a reviewer recognise where judgement enters the model and where arithmetic takes over. It also makes accidental replacement of a formula easier to spot.
Reconcile at more than one level
Check individual extensions, package subtotals and the overall total. A grand total alone is a poor review tool. Section summaries help identify whether cost has moved between packages or disappeared from the model.
Keep rounding conventions consistent. Where a worked example requires full precision between steps, round the displayed result without prematurely rounding the underlying calculation.
Make changes understandable
Before editing a shared estimate, agree how the new version will be identified and reviewed. Preserve the description of what changed and why. A copied file with a new date is less useful than a clear revision note linked to the affected scope.
A good spreadsheet does not need to imitate every capability of a specialist estimating system. It needs to make the work understandable, preserve the assumptions and support a reliable check.