A machine has an actuating member constantly exactly moved on a repeat cycle coincident with the machine operating cycle. A switching device is positioned movable by predetermined signal means from a retracted position not contacting nor influenced by the actuating member and an extended position contacting and moving under control of the actuating member. Thereby, for instance, the switching device in the extended position as controlled by the actuating member may stop operation of the machine at a particular phase of the machine operating cycle and despite the time of the signal means, yet the switching device may be retained out of contact with the actuating member during normal machine operation.