A computer-implemented method for calibrating a scanning system in an additive manufacturing device, the method comprising: directing a scanner beam from the scanning system to apply scan markings at a plurality of predefined locations in a scanning area; acquiring, using an image acquisition assembly (436, 503), a scan image comprising image scan markings corresponding to the scan markings; determining scanner corrections based on position of the image scan markings and the predefined locations in the scanning area; and calibrating the scanning system using the scanner corrections, characterised by: acquiring, using the image acquisition assembly (436, 503), a reference image comprising a plurality of image reference markings corresponding to a plurality of reference markings on a first surface of a calibration plate (448, 501) that is positioned parallel to a scanning area of the scanning system and in the additive manufacturing device; and determining an error function, wherein the error function represents a difference between the plurality of image reference markings in the reference image and the plurality of reference markings on the first surface of the calibration plate, wherein the directing of the scanner beam is performed when the calibration plate (448,501) is not in the scanning area, wherein the acquiring of the reference image is performed using the image acquisition assembly (436,503) in a reference position, and wherein the determining of the scanner corrections is further based on the error function. directing a scanner beam from the scanning system to apply scan markings at a plurality of predefined locations in a scanning area; acquiring, using an image acquisition assembly (436, 503), a scan image comprising image scan markings corresponding to the scan markings; determining scanner corrections based on position of the image scan markings and the predefined locations in the scanning area; and calibrating the scanning system using the scanner corrections, characterised by: acquiring, using the image acquisition assembly (436, 503), a reference image comprising a plurality of image reference markings corresponding to a plurality of reference markings on a first surface of a calibration plate (448, 501) that is positioned parallel to a scanning area of the scanning system and in the additive manufacturing device; and determining an error function, wherein the error function represents a difference between the plurality of image reference markings in the reference image and the plurality of reference markings on the first surface of the calibration plate, wherein the directing of the scanner beam is performed when the calibration plate (448,501) is not in the scanning area, wherein the acquiring of the reference image is performed using the image acquisition assembly (436,503) in a reference position, and wherein the determining of the scanner corrections is further based on the error function. acquiring, using the image acquisition assembly (436, 503), a reference image comprising a plurality of image reference markings corresponding to a plurality of reference markings on a first surface of a calibration plate (448, 501) that is positioned parallel to a scanning area of the scanning system and in the additive manufacturing device; and determining an error function, wherein the error function represents a difference between the plurality of image reference markings in the reference image and the plurality of reference markings on the first surface of the calibration plate, wherein the directing of the scanner beam is performed when the calibration plate (448,501) is not in the scanning area, wherein the acquiring of the reference image is performed using the image acquisition assembly (436,503) in a reference position, and wherein the determining of the scanner corrections is further based on the error function.