A course of a position of a positioning device is determined as a laser beam welds a workpiece at a focus area of the laser beam. The positioning device is configured to position the focus area of a laser beam on a workpiece such that a joint is formed on the workpiece. A course of the joint on the workpiece from the determined course of the position of the positioning device is estimated, and a deviation between the determined course of the position of the positioning device and the estimated course of the joint on the workpiece is calculated. The deviation represents a parameter related to the precision of the seam position control.