Tensile force F is applied by means of shackles 1 and 2 and steel ball 3 to piston 4 of the hydraulic capsule. Through diaphragm 5, piston 4 applies pressure to the liquid. This pressure is transmitted to Bourdon tube 6 which tends to straighten out. The free end of tube 6 is connected through a flexible link, running over pulley 7, to spring 8. Pulley 7 turns about fixed axis A and is rigidly attached to pen 9 which registers the measured forces on chart paper a.