An absolute 2D position-sensing device is usable to measure the position of a first element with respect to a second element. Related systems are also provided. The present method is simple, the coupling reaction is fast, pure copolymers are produced and the molecular weight, graft number and grafting position can be controlled to a greater extent than in existing methods. Then, the image is displayed in a part of the image display area that corresponds to the area of the representation of the partitioning. Consequently, the blade remains contained inside the net, and blade containment is improved. The image forming apparatus further including a door which is opened when consumable material is supplied, and a door openedclosed sensor configured to detect the door opening or door closing.