mounted on a flexible material 70 which is positioned in a compact spiral arrangement along the inside circumference of the probe housing the electronics include light emitting diodes 26 for transmitting the optical measurement signals 16 a plurality of photodiodes 28 for receiving the switch on signal 18 and indicators 44 in the form of red and green light emitting diodes for indicating the mode the light emitting diodes 26 photodiodes 28 and indicators 44 are distributed around the circumference of the probe behind a glass window 30 the stylus 11 is mounted on a kinematic seat inside the housing the kinematic seat comprises three vee shaped grooves each formed between a pair of ball bearings 72 the stylus has three cylindrical members 74 extending radially from its upper end which are urged into contact with the vee shaped grooves by a spring 76 this defines the rest position of the stylus 11 such an arrangement is well known and described in u s pat no 4 153 998 when the stylus is in this rest position an electric circuit which passes in series from one vee shaped groove to the next adjacent one is completed each member is insulated from the stylus and other members and completes the circuit between the two sides of each respective vee shaped groove deflection of the stylus results in at least one of the members breaking contact with the ball bearings and thus breaking the circuit as described in u s pat no 4 153 998 the breaking of the circuit is used to provide an input pulse to an automatic switching arrangement and thereby indicate that deflection of the stylus has occurred in the present invention this arrangement may.