How are pollen counts done?

We use an air-sampling device called a Burkard spore trap to capture airborne pollen on a glass slide, which we stain with a dye and count using a microscope. During the grass pollen season, a slide is removed from the trap at the same time each day and counted twice. The first time we count all types of pollen on the slide and the second time just the grass pollen (which has a distinctive shape). Our daily pollen count is a report of grass/all kinds of pollen (as grains per cubic metre of air) caught in the trap in the previous 24 hours. Our pollen forecast is based on this count and on the weather forecast for the next 6 days.