[AIVC, Air infiltration and ventilation glossary, 1992]:a) A method of measuring the air change rate using tracer gas and a two channel pump. One channel dispenses tracer gas from a bag of known volume, the other draws room air into a sample bag. The final concentration of tracer in the room air and the amount of tracer gas used, enables the calculation of the average inverse air change rate.b) A method of measuring the air change rate by which tracer is discharged into a sample volume and mixed. Sample bags are inflated with room air at intervals and the concentration of tracer measured.