Abstract: A rolling mill has a transducer for measuring the separation of a movable part of the mill from the fixed part of the mill. The transducer comprises a magnetostrictive element secured to one end of the fixed part, a transmitter for transmitting magnetostrictive signals into the element, a receiver for receiving signals reflected back along the element and a magnet secured to the other part which produces a magnetic field which serves to reflect the signals along the element. A timer measures the time interval between transmitting the energy and receiving the echo and this is representative of the distance between the two parts of the rolling mill.