A densitometer is described which is equipped with an extendable and retractable measuring head driven by an electric motor. In the retracted rest position, a measuring diaphragm is visible to the user and the instrument may be positioned. In the extended working position the measuring head covers the...http://www.google.fr/patents/US4645350?utm_source=gb-gplus-shareBrevet US4645350 - Densitometer
