The feasibility of a device to enable precise and repeatable calibration of single-breath lung diffusion (DLCO) instruments will be investigated. The calibrator will enable the accuracy of DLCO instruments to be verified between pulmonary laboratories, allowing greater confidence in a diagnosis based on the single breath DLCO test. This study will verify the performance of a unique gas collection and mixing system which will allow generation of precise carbon monoxide (CO) and Helium (HE) gas fractions without using gas analyzers. This will allow production of a DLCO calibrator which will not require any calibration of its own.