face so that there is no danger of the weight of the crane causing the top of the rock face to collapse in operation two or three operators are normally required to work the wall face an observer or monitor stands at a distance away from the wall face or rock face on a quarry floor or perhaps is situated on an opposite face of the quarry and may have a telescope or a pair of binoculars or a close up tv camera through which to observe the condition of the face and the wall brush 10 the monitor determines whether all the loose material has been dislodged by the wall brush 10 from a particular section of the rock face the monitor communicates his observations on a walkie talkie or another means of communication to a second operator who is standing near the crane above the wall face the second operator then tells a crane operator whether to reciprocate the wall brush 10 on the same section of the rock face again or to move the wall brush 10 to another section of the rock face because the first section had been cleared of loose material if the crane operator has a set of earphones and a microphone through which to communicate with the monitor then only two operators are necessary to work the wall face in a large operation it may be possible to have a single observer using closed circuit television screens in a central control.