Summary and detailed measurement

	Summary bill	Detailed measurement
Nature	contract document	supporting calculation
Content	items, units, quantities	dimensions, measurements, formulas
Recipient	the tenderers	the designer
Contractual value	yes	in principle no
Circulation	with the tender documents	stays with its author

The summary bill is the one the rules define: it divides the works into items and states for each the quantity or the manner of determining the price. It is the document contractors price.

The detailed measurement is the route to it. It contains surveys, dimensions, area and volume calculations and deductions, item by item. Every quantity in the summary bill finds its justification there.

A frequent question, and the answer lies in the nature of the two documents. One is contractual, the other a working document.

Issuing the detailed measurement would amount to contractualising a calculation. What the contract commits are items and quantities, not how the designer arrived at them. An erroneous intermediate calculation that nonetheless yields the right quantity should not open a discussion.

The detailed measurement contains working assumptions. They are useful to their author and misleading to a third party, who might take them for commitments.

It was not designed to be read by others. Its form is free, its conventions internal, and its interpretation by an outside reader uncertain.

Four uses, all real, and all to its author's benefit. The detailed bill serves to prepare, check, update and defend the quantities.

Justifying a disputed quantity. Where a contractor challenges a figure, the detailed measurement allows the calculation to be revisited and settled quickly.

Reworking the bill after a change of project. Without it, a change forces a full recalculation. With it, only the affected parts are reworked.

Documenting the method. The deduction rules applied, the conventions adopted and the assumptions about unsurveyed parts appear there. That is what makes it possible, two years later, to know why a quantity is what it is.

Protecting the designer. In the event of a claim, a coherent detailed measurement demonstrates the seriousness of the approach. Its absence makes defence far harder.

In private contracts the distinction remains but its framing changes. It then rests on the contract rather than on regulation.

No text defines what the documents must be: the contract says so. Practices therefore vary commonly, and the contractual status of one document or another can be ambiguous.

Two precautions are worth taking. State expressly in the contract which documents are contractual, and in what order of priority they apply in case of contradiction.

That hierarchy of documents is the first thing to reach for when a dispute arises, and drafting it costs a few lines. It is settled in a single clause at drafting stage.

A practical point often neglected.

The detailed measurement has value only if it can be found and read later. Three habits suffice.

Keep it with the version of the framework used, or the measurement rules applied become undeterminable.

Date it and tie it to the version of the project it relates to, a measurement prepared on drawings since revised no longer having the same meaning.

Keep it as long as liability can be engaged, which in construction runs to years after acceptance.

Three rules.

Do not issue the detailed measurement with the tender documents, save by a conscious and contractualised decision.

Keep it nonetheless as though it will be read, because it will be if a dispute arises.

Keep the detailed measurement, the summary bill and the version of the framework together, those three elements having value only in combination.