A device used to measure the function of the respiratory system in adults and compliant children. It usually includes a spirometer with volume-sensing (e.g., rolling-seal, bellow) and flow-sensing (e.g., pneumotachometer) devices, a gas analyser for evaluation of absolute lung volumes and gas-diffusing capacity of the lungs, and computer capabilities for data processing and recording; a total-body plethysmograph to measure both lung volumes and airway resistance may be included. The device is mostly used for outpatient or presurgical screening, and may also be used in the diagnosis and evaluation of common diseases in older children [e.g., asthma, cystic fibrosis (CF), chest deformities].