A method of measuring the volume (V) of a gas in a container (20) comprises varying the container volume according to a sine wave between a minimum and a maximum value, the variation being made at a constant frequency but at varying amplitude, to obtain a predetermined pressure difference (.DELTA.p),...http://www.google.de/patents/US4713966?utm_source=gb-gplus-sharePatent US4713966 - Method and apparatus for volume measurement
