7. In this Part, “face working” in relation to a working face at which supports are systematically withdrawn means all that part of the mine between the face and the front line of the packs, if any, or the last row of supports for the time being maintained whichever is further from the face and in relation to a working face at which supports are not systematically withdrawn means all that part of the mine between the face and a line parallel to it and 3.7 metres distant from it.