flexion locking surfaces 30 and 32 are machined directly onto or into the upper and lower steels 10 and 12 so that these two surfaces form in effect a slot into which the locking wedge 24 fits tightly as will be appreciated the manner in which the locking wedge is mounted allows it to 34 float 34 to some extent so that it centralizes between the locking surfaces 30 and 32 the locking surfaces 30 and 32 on the two steels are preferably flat which means that they can be easily ground to high accuracy before final assembly of the caliper thereby avoiding the need for final adjustment by filing the locking surfaces a further important feature of the caliper is that the pivotal connection between the two steels comprises two spaced apart pivot points 16 and 18 which thus provide the joint with dual pivots this allows it to follow the true centre of rotation of the patient 39 s knee it is to be noted that in the extended position of the steels shown in fig1 the plunger or piston 36 projects outwardly from its cylindrical chamber 38 so as to serve as a push button this makes for easy operation of the caliper to release.