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(a)in relation to a working face at which supports are systematically withdrawn, means all that part of the mine between the face and the front line of the packs, if any, or the last row of supports for the time being maintained,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(b)in relation to a working face at which supports are not systematically withdrawn, means all that part of the mine between the face and a line parallel to it and 3.7 metres from it.