A single Air Particle Count or Indoor Air Quality Test (IAQT) measures the volume of airborne particulate within one cubic meter (1m3) of air within the room. The ISO standard requires that a number of tests be taken at different positions in the room depending on the size and shape of the room. The sum of the results is then divided, and the average is the volume per cubic meter for that room (at least 90% of the room should be subject to air quality analysis).