Explanation : The arrangement of two flanges A and B placed at a distance on the shaft is as shown. Flange A carries a scale while flange a pointer. When a torque is applied on the shaft it causes angular displacement of pointer relative to the scale due to the angular twist. The deflection of the shaft may be read off directly when the shaft is stationery. However this is not possible if the shaft is rotating. In such cases, stroboscope is used. The flashing light of the stroboscope is applied onto the scale and the flashing frequency is adjusted till a stationery image is obtained. The scale reading can now be taken for measuring the angular twist. This method is simple and inexpensive. However, the accuracy of measurement is poor.