Robust case 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 lead exit (with connector for testing). Note: 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.