Miniature peak flow meter is compact, portable diagnostic device of beeper size. It consists of two bodies which create a curved cylinder inside which moves a rotational piston by means of rotation. The resistance to that movement is achieved by a specially created torsion spring. The mouthpiece is folded...http://www.google.de/patents/US5613497?utm_source=gb-gplus-sharePatent US5613497 - Miniature peak flow meter
