Apparatus for reliably determining the position of an object regarding a relative movement between the object and a path, comprising: a detector attached to or integrated in the object, at least one marker being located along the path, wherein the at least one marker is detected by the detector within its spatial detection range for determining the position of the object relative to the marker, generating means for providing a definable graphic representation (7, 8) or graphic representation sequence, wherein said graphic representation (7, 8) or graphic representation sequence is detected by the detector within its spatial detection range, and evaluating means for verifying a coincidence or relationship of the provided graphic representation (7, 8) or graphic representation sequence with corresponding data detected by the detector, for verifying whether a software within the detector is still correctly functioning or is possibly frozen or hung up or has a time shift/delay, wherein the generating means comprise at least one light source (9, 10) emitting at least one definable light colour or light colour spectrum for illuminating a correspondingly coloured graphic representation (7, 8) or graphic representation sequence provided by the generating means, so that depending on the at least one illuminating light colour or light colour spectrum the graphic representation (7, 8) or a part of the graphic representation is visible by the detector with a predefinable intensity and/or colour or not, and wherein the coloured graphic representation (7, 8) or graphic representation sequence and the at least one marker are identical and are realized by a data matrix code or data matrix codes. a detector attached to or integrated in the object, at least one marker being located along the path, wherein the at least one marker is detected by the detector within its spatial detection range for determining the position of the object relative to the marker, generating means for providing a definable graphic representation (7, 8) or graphic representation sequence, wherein said graphic representation (7, 8) or graphic representation sequence is detected by the detector within its spatial detection range, and evaluating means for verifying a coincidence or relationship of the provided graphic representation (7, 8) or graphic representation sequence with corresponding data detected by the detector, for verifying whether a software within the detector is still correctly functioning or is possibly frozen or hung up or has a time shift/delay, wherein the generating means comprise at least one light source (9, 10) emitting at least one definable light colour or light colour spectrum for illuminating a correspondingly coloured graphic representation (7, 8) or graphic representation sequence provided by the generating means, so that depending on the at least one illuminating light colour or light colour spectrum the graphic representation (7, 8) or a part of the graphic representation is visible by the detector with a predefinable intensity and/or colour or not, and wherein the coloured graphic representation (7, 8) or graphic representation sequence and the at least one marker are identical and are realized by a data matrix code or data matrix codes.