Method for determining a closed trajectory by means of a laser and a laser light sensor with a planar measuring field, wherein the measuring field has a system of coordinates with an X coordinate axis and a Y coordinate axis at right angles to the X coordinate axis, the laser light sensor being designed for sensing on the measuring field the X coordinate and Y coordinate of the position of the laser light spot of the laser light beam of the laser impinging on the measuring field, the method comprising the following steps: rotationally fixed linking of the laser to a first shaft, which is connected to a second shaft via a coupling, so that a rotation of the first shaft can be transmitted to the second shaft and vice versa, rotationally fixed linking of the measuring field to the second shaft, the measuring field being linked to the second shaft in such a way that the Y coordinate axis and the X coordinate axis are oriented substantially at right angles to the axis of rotation of the second shaft, alignment of the laser in such a way that the laser light beam that can be generated by the laser is aligned parallel to the axis of rotation of the first shaft and can impinge on the measuring field, rotation of the first or second shaft (28, 32) in a predetermined direction of rotation by at least 90 degrees and irradiation of the measuring field with the laser light beam of the laser during the rotation, sensing by the laser light sensor of the X coordinates and Y coordinates of at least three positions of the laser light spot on the measuring field that the laser light spot assumes on the measuring field during the rotation in step, determination of the X coordinate sensed first in time and the Y coordinate sensed first in time and assignment of a predetermined value of the angle of rotation to the X coordinate sensed first in time and to the Y coordinate sensed first in time, determination of the closed trajectory by means of the X coordinates sensed in step and/or the Y coordinates sensed in step; wherein, in step, furthermore the sensed X coordinates and/or the sensed Y coordinates are used as a basis for determining a representation of the trajectory which is parameterized by the angle of rotation of the first or second shaft (28, 32) that is measured in the direction of the predetermined direction of rotation, starting from the predetermined value of the angle of rotation. rotationally fixed linking of the laser to a first shaft, which is connected to a second shaft via a coupling, so that a rotation of the first shaft can be transmitted to the second shaft and vice versa, rotationally fixed linking of the measuring field to the second shaft, the measuring field being linked to the second shaft in such a way that the Y coordinate axis and the X coordinate axis are oriented substantially at right angles to the axis of rotation of the second shaft, alignment of the laser in such a way that the laser light beam that can be generated by the laser is aligned parallel to the axis of rotation of the first shaft and can impinge on the measuring field, rotation of the first or second shaft (28, 32) in a predetermined direction of rotation by at least 90 degrees and irradiation of the measuring field with the laser light beam of the laser during the rotation, sensing by the laser light sensor of the X coordinates and Y coordinates of at least three positions of the laser light spot on the measuring field that the laser light spot assumes on the measuring field during the rotation in step, determination of the X coordinate sensed first in time and the Y coordinate sensed first in time and assignment of a predetermined value of the angle of rotation to the X coordinate sensed first in time and to the Y coordinate sensed first in time, determination of the closed trajectory by means of the X coordinates sensed in step and/or the Y coordinates sensed in step;