The figures you always look up at the worst moment

Waste allowances

The percentage to add to the net area before ordering. Underestimated, it costs a second delivery; overestimated, it sleeps in the back of the van.

Paint coverage rates

One figure per litre and per coat. The coat is the unit that matters: two coats on a wall means twice the area.

Partition thicknesses

In the French designation, the first number is already the finished thickness. A 98/48 is 98 millimetres, not 48.

Accessibility dimensions

The six or seven dimensions you recheck on every project, gathered on one page.