Measurement errors and their consequences

Type	Description
The omitted item	necessary work does not appear in the bill
The wrong quantity	the item exists, its quantity is incorrect
The unsuitable unit	the unit does not match the nature of the work
The item without prescription	the bill lists work the specification does not describe
The duplicate	the same work appears in two places

The omitted item is the costliest, the duplicate the most insidious. The first emerges during construction, the second inflates tender prices without anyone noticing.

Here the distinction between provisional and lump-sum quantity takes its full effect. It determines who bears the gap observed.

Under a provisional quantity, a wrong quantity corrects itself naturally: payment follows quantities actually executed, at the agreed rate. The error affects the budget forecast, not the parties' rights.

Under a lump-sum quantity, the same error does not correct itself. The quantity being fixed, the difference stays with whoever the contract designates.

The omitted item escapes both regimes. Work absent from the bill has neither quantity nor price. It will be carried out as additional work, negotiated without competition.

These regimes are set out in the article on provisional and lump-sum quantities. The allocation of risk is explained there regime by regime.

Three parties, three different exposures. The author of the bill, the contractor and the client do not risk the same thing.

The client bears the economic cost of most errors: excess on provisional quantity, additional work on an omitted item, inflated price from a duplicate.

The designer bears the risk of a claim. A manifestly incomplete bill may engage their professional liability, and that is where the detailed measurement takes its protective role, covered in the article on summary and detailed measurement.

The tenderer bears a duty of vigilance. Belgian public procurement rules require reporting errors discovered, under conditions covered in the article on who bears the risk of a quantity error.

That duty to report is the most structuring Belgian feature of the subject. It prevents a contractor from speculating silently on an error spotted.

It deserves separate treatment because it escapes the usual checks. It is the missing item, which arithmetic checking does not catch.

The same work priced in two places produces a total above the real cost. No item is wrong taken alone, and the consistency check between specification and bill does not catch it where the two items refer to distinct prescriptions.

It is caught by reading, looking for overlaps between trades. The risk zones are known: junctions between shell and finishes, between services and finishes, between building and external works.

Four checks, from quickest to most demanding. They are run in that order and stop as soon as a gap appears.

The cross-check of indexes, which catches orphan items and unpriced prescriptions.

The check of units, item by item, against the description.

The check of orders of magnitude, relating principal quantities to the area or volume of the project. An anomalous ratio signals an entry or conversion error.

Reading the overlap zones, the only effective method against duplicates.

Four rules.

Never treat a bill as a fixed document. It evolves with the project and must be rechecked at each iteration.

Check orders of magnitude before details. An error by a factor of ten shows in a minute and costs months.

Document the assumptions of uncertain items, so that a later difference can be explained.

Report an error spotted, including where it is favourable. In public contracts the duty exists and silence exposes.