A drill guide uses a hole in a layer to guide a drill along an axial trajectory while permitting off-axis excursions of the drill during use. The sensor electrodes disposed on the substrate. The hot air passageway has a first heat exchange area. Thus the PIFA antenna is firmly retained on the plastic base. The second anti-reflective layer is removed using a third plasma comprising chlorine. The covering has an inner surface that is located on the LED light emission unit’s side and an outer surface opposite to the inner surface.