Burkard 7 day recording spore traps are used at both sites. The spore traps are mounted on rooftops and connected to mains. An air flow of 10 litres per minute is sucked into an orifice or slit in the body of the instrument, by means of a vacuum pump and this air moves over a sticky cellulose strip which is wound around a drum inside the casing. The drum moves the cellulose strip past the orifice at the constant rate of 2mm per hour, by means of a clockwork mechanism. The large vane on the spore trap catches the wind and directs the orifice into the wind, thus maximizing the pollen catch. The airflow rate is checked with an airflow metre each week. At the end of each seven day cycle, the cellulose strip is removed and replaced with a fresh strip. The harvested strip is divided into seven 48mm sections, mounted onto slides and read by means of a light microscope. Each slide represents one 24 hour period and these raw scores are converted to absolute scores by means of a conversion or correction factor, which takes into account the size of the microscope aperture. The health risk for allergy to pollen or fungal spores is calculated according to a scale which has values for the pollen taxa. These pollen taxa are usually divided into the categories; grasses, trees and weeds. Significant or threshold levels for fungal scores vary according to the fungal taxon or type. Pollen and fungal spore levels are usually reported as ‘high’, ‘moderate’ or ‘low’.