The fewest sampling points allowed comes from the standard's Table A.1 by floor area, chosen so that there is 95 percent confidence or better that 90 percent or more of the area meets the class limits (rounding up to the larger table entry when the area falls between two; for unidirectional flow the area may be the cross-section at right angles to the flow, otherwise the plan area); above 1 000 square metres Formula A.1 gives the minimum. The room or zone is then split into that many equal-area sections, one representative point is picked in each, and the probe is set at working height or another specified point at each. Further points may be added where positions are critical, their number and placement agreed and specified; further sections may be added to make the split even; and in rooms without unidirectional flow a point straight under an undiffused air supply may not be representative.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.