A method and a device for verifying one or more safety volumes for a movable mechanical unit positioned in an environment, wherein a world-coordinate system is defined in relation to the mechanical unit and in relation to the environment of the mechanical unit. The method includes storing a description of one or more safety volumes defined in relation to the world-coordinate system, and repeatedly determining position and orientation of a portable display unit in relation to the world-coordinate system, determining a graphical representation of the safety volumes based on the description of the safety volumes and the position and orientation of the portable display unit, overlaying the graphical representation of the safety volumes on a view of the real mechanical unit and its environment to provide a composited augmented reality image, and displaying the augmented reality image on the portable display unit.