For swift and secure determination of a measurement error a first digital image is obtained using an image sensor, wherein a line of sight of an optical arrangement is oriented in a first face direction. A characteristic image area in the first digital image on an image sensor is determined. A second digital image is then taken with a line of sight of the image sensor oriented in a second face and the characteristic image area defined in the first image is searched in the second digital image, the first or the second digital image is rotated in the image plane by 180° . Then in the second digital image the position of the characteristic image area is determined. And offset between the characteristic image area in the first digital image and the characteristic image area in the second digital image is determined.