Apparatus is provided for a fiber optic gyro. The rotor includes at least one endring defining a plurality of openings. The second epicyclic gear group has two degrees of freedom, with the second epicyclic gear group including a first gear coupled to the input shaft, a second gear coupled to the second output shaft and a third gear. A magnet coil yoke abuts the elastomer element and is fixed to at least one of the recesses. To be able to carry out measurements without a fixed reference, it is proposed that, independently of a reference that is independent of the patient, the position of the measuring device is measured by means of a position-determining sensor that is in a fixed relationship to the measuring device. The Bentonite reduces the hydraulic conductivity of magnesium peroxide, thereby reducing the rate of magnesium peroxide disassociation.