The outdoor air is sampled for the previous 24-hour period using a device called a Roto-rod. The Roto-rod samples the air every 10 minutes and the airborne mold and pollen granules are captured on glass rods. The glass rods are then retrieved daily and stained before being placed under a microscope. The individual pollens and molds are then counted and classified.
The count is reported as the number of pollen granules per cubic millimeter of air/24 hours and interpreted as absent, low, moderate, or high. The mold spores are similarly counted and reported also as absent, low, moderate, or high.