A sensor device is for performing rapid optical measurement of distances according to the confocal optical imaging principle in order to determine distance values andor height values of a surface. Adjustments to the amount of such offset of the screw axis can be made in steps as the outer edges of the flights on the conveying screw wear. Additional embodiments may include first and second members attached to the back of the case where an end of the support element is pivotally attached between the first and second members, so that the element supports the case when the musical instrument is removed from the case.