Arrangement for marking and detecting the marking for determining track sections reliably and accurately with respect to position for the purpose of maintaining rails, wherein means are provided for optical detection of measuring points, characterized in that - a sensor unit for detecting measuring points located next to a rail has at least two independent detector units (I, II) measuring in a non-contacting manner based on different measurement principles, • wherein for a first measurement principle the sensor unit includes an optical sensor having spectrally selective sensitivity, and • for a second measurement principle the sensor unit includes an identification detector for individual identification of measuring points, - the measuring points are constructed as angle elements having at least two legs (41, 42), wherein a first, vertically oriented leg is detachably fastened to the rail, and a second, horizontally oriented leg is provided with a coating emitting in a narrow spectral band for the spectrally selective sensor and with an identification value carrier for the identification detector, and - the sensor unit is adjustably arranged at a device which can travel on tracks in such a way that the coating emitting in a narrow band and the identification value carrier on the second, horizontal leg of each angle element are detectable simultaneously, when the independent detector units (I, II) of the sensor unit are positioned in the same direction with the movement of the device which can travel on tracks parallel to the rail over one of the angle elements fastened to the rail as measuring points. - a sensor unit for detecting measuring points located next to a rail has at least two independent detector units (I, II) measuring in a non-contacting manner based on different measurement principles, • wherein for a first measurement principle the sensor unit includes an optical sensor having spectrally selective sensitivity, and • for a second measurement principle the sensor unit includes an identification detector for individual identification of measuring points, • wherein for a first measurement principle the sensor unit includes an optical sensor having spectrally selective sensitivity, and • for a second measurement principle the sensor unit includes an identification detector for individual identification of measuring points, - the measuring points are constructed as angle elements having at least two legs (41, 42), wherein a first, vertically oriented leg is detachably fastened to the rail, and a second, horizontally oriented leg is provided with a coating emitting in a narrow spectral band for the spectrally selective sensor and with an identification value carrier for the identification detector, and - the sensor unit is adjustably arranged at a device which can travel on tracks in such a way that the coating emitting in a narrow band and the identification value carrier on the second, horizontal leg of each angle element are detectable simultaneously, when the independent detector units (I, II) of the sensor unit are positioned in the same direction with the movement of the device which can travel on tracks parallel to the rail over one of the angle elements fastened to the rail as measuring points.