The counter is set up as its maker instructs, including a zero count check. The probe faces into the airflow, or straight up where the flow direction is uncontrolled or unpredictable. The room is brought to the normal conditions of the chosen occupancy state before any sample is drawn, and at least the calculated volume is drawn for each sample at each point. A count above the limit that stems from an identified abnormal event may be set aside, noted as such in the report, and replaced by a fresh sample; where such a count is put down to a fault in the room or its equipment, the recommended course is to find and remedy the cause and retest that point, the points around it and any others affected, with the decision written down and justified.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.