Abstract: The invention relates to a device for alignment of a first component (1; 25) and a second component (2; 26) in a predetermined relation to each other, comprising first measuring unit (7; 7?; 7?) arranged to be mounted on said first component (1; 25) and comprising a light-source (9) for generation of light-radiation (10; 10?) with a predetermined pattern in direction towards a second measuring unit (11; 11?) arranged to be mounted on said second component (2; 26) and also comprising a second light-source for generation of light radiation (13; 13?) with a predetermined pattern in direction towards said first measuring unit (7; 7?; 7?), were each of the measuring units (7, 11; 7?; 7?, 11?) comprises a detection device for emitted light radiation. The invention is characterized in that each of the measuring units (7, 11; 7?; 7?, 11?) comprises at least one reference component (18a, 18b, 19a, 19b) which during said alignment is connected with a predetermined position on respective component (1, 2; 26, 26).