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Frequency meter or - a relay according to patent 407309 with two oscillation organs of different natural frequency, whose schalldruecke in the opposite direction to the movable part of an act schallstaerkemessers
Frequency meter or - a relay according to patent 407309 with two oscillation organs of different natural frequency, whose schalldruecke in the opposite direction to the movable part of an act schallstaerkemessers