1. The heat source, formed by the heating element (30) is located in the direction of the bisector (49) of the angle $g(a) which is formed at the edge (46, 47) of the chamfer (40) that lies nearest to the heating element (30).

Die vom Heizelement (30) gebildete Wärmequelle liegt in Richtung der Winkelhalbierenden (49) des Winkels $g(a), der an der am nächsten zum Heizelement (30) liegenden Kante (46, 47) der Fase (40) eingeschlossen ist.