Position indicator through acoustics

An assembly comprising a body 104 movable relative to a tubing section102; a signal generator 108 coupled to the body and operable for detecting a detectable portion 106 of the tubing section in response to relative movement between the body and the tubing section. The signal generator is an electronic signal generator and includes a sensor to sense the proximity of the detectable portion and is operable to generate a pressure wave in response to detection of the detectable portion corresponding to a first location of the body relative to the tubing section. In response to the sensor sensing the proximity of an additional detectable portion it generates an additional pressure wave differentiable from the first pressure wave and corresponding to a second location of the body relative to the tubing section. The sensor may be magnetic or RFID. Alternative disclosed signal generators include striking hammers and floodable atmospheric chambers to indicate one or more positions