Robust case with wall thickness of 5 mm either in seawater resistant aluminum or in stainless steel - shaft in stainless steel - rotating components with permanent magnet in front chamber - electronic circuit with ASiC and Hall elements and interface components fitted within main chamber, separated from rotating components by a metallic wall - integral counter for the acquisition of revolutions, with non - volatile storage - optional potting against water jets (IP 69K) - electrical connections via round plug or lead exit. Note (TMA, TMN): The device restores the position value in case the supply voltage is cut off, provided that the shaft is not deflected by more than ±90° during the interruption of the supply voltage.