An estimate can look impressively precise and still be difficult to defend. A total with two decimal places tells us how the spreadsheet is formatted. It tells us very little about the quality of the scope, quantities or assumptions beneath it.
The more useful question is whether another estimator can follow the reasoning without having to reconstruct the entire job.
Make the basis visible
A concrete rate is not just a price per cubic metre. It represents a work method, a crew, an expected output, a supply basis and a set of inclusions. If pumping is included in one quotation and excluded in another, identical-looking rates describe different things.
The basis should travel with the number. Record the source, the unit, the price date and the scope boundaries where they can be reviewed. A short, specific note is often more useful than another layer of spreadsheet detail.
Put judgement where it can be challenged
Productivity, waste and access assumptions deserve attention because they connect the model to the work. A reviewer should be able to ask what changes if output falls, if the work sequence shifts, or if a supplier qualification is accepted.
Those conversations become harder when allowances are hidden inside rounded rates. Separating the inputs makes the consequences visible. It also makes revisions less dependent on the person who first built the estimate.
Review the explanation, then the total
An arithmetic check is necessary, but it is only one part of a review. A missing work item can coexist with perfectly functioning formulas. A duplicated allowance can appear twice without either formula being wrong.
Start with scope completeness, then examine the assumptions, and finally reconcile the arithmetic. The aim is an estimate that can support a decision and explain what might change it.
A defensible estimate does not eliminate uncertainty. It makes the uncertainty easier to discuss.