Abstract: Apparatus which monitors the extent to which a mechanical valve (2) is opened which employs a rotary position transducer (5). The rotary position transducer (4) provides a signal representative of valve (2) position to a signal processor (10, 140 for analysis. The signal processor (10, 14), in turn, activates various announciator lights (122, 124) which provide a visual indication of valve (2) position and sends signals to other apparatus (21) associated with the valve (2). Also provided is a mounting (30, 32, 44, 102, 104) for apparatus which monitors the extent to which a mechanical valve (2) is opened.