When buying a spirometer make sure that the manufacturer or dealer guarantees that the equipment meets the specifications issued by the ATS (American Thoracic Society) and/or the ECCS and ERS (European Respiratory Society).
Most electronic spirometers contain a device for measuring gas flow, i.e. volume displacement per unit of time. The flow can be measured from the pressure drop across a tube with known resistance to flow (pneumotachometer or pneumotachograph of type Fleisch or Lilly ), by measuring the temperature change or heat transfer from an electrically heated wire (anemometer ), or by counting the number of revolutions per unit of time of a small turbine. The volume displacement is then computed by integrating flow with respect to time. All electronic spirometers are equipped with a chip, which performs the integration. In addition it computes the forced expiratory volume in one second.