A Bill of Quantities is meant to describe the design in measurable terms. When bidders or reviewers find that the quantities do not match the drawings, confidence in the whole document drops. In most cases the measurement itself was done correctly. The mismatch comes from how the measurement was set up.
1. The drawing set moved on. Quantities were taken from one revision and the drawings were updated afterwards. Every BOQ should state the drawing list and revision it was measured from, so a mismatch can be traced to a date rather than argued about.
2. The measurement rules were never stated. Openings deducted or not, laps included or not, areas measured net or gross. Two correct take-offs can differ simply because they followed different rules. Agree the rules, then write them into the preambles.
3. Item descriptions don't say what was measured. "Blockwork walls" can mean several thicknesses, finishes and heights. If the description does not carry the characteristics that change the price, the quantity cannot be checked against the drawing.
4. Scope sits between packages. Interfaces such as wall-to-ceiling junctions, external works edges or MEP builders' work are easy to leave out of every package, or to include in two. A package boundary list prevents both.
5. Missing information was measured as if it existed. Where the design is not yet defined, an assumed quantity can look as firm as a measured one. Assumptions should be marked as such and listed, so everyone knows which numbers will move.
A structured take-off workbook makes each of these visible: drawing references against every item, rules stated once, assumptions flagged. The aim is not a BOQ that can never change. It is one where every quantity can be traced back to the design that produced it.