Re. Calibration of Peak Expiratory Flow

(PEF) measuring devices There are increasing numbers of devices coming onto the market for measuring PEP and of papers assessing their performance. In these papers a number of different ways of calibrating the devices have been used, as discussed in your correspondence columns [1]. What is the best way to calibrate a peak flow (PP) meter for clinical use? It seems not to be realized that compared with a large pneumotachometer, portable PP meters have an appreciable resistance to airflow. This will have a measurable effect on the very thing being measured, i.e. the PEP. When WRimrr and McKEiutow [2J calibrated their original instrument in 1959 they used a form of calibration which allowed for this. Having calibrated