to clamp the outer sides of the workpiece in cooperation with jaw 13 of the main scale 11 the slider 12 also has on the upper edge of the same end thereof a jaw 17 for measuring the internal dimension by contact with the inner sides of the workpiece in cooperation with the jaw 14 of the main scale 11 the slider also has at the lower edge of the other end thereof a finger grip 18 projecting downward in a semicircular fashion and on the surface opposite to this finger grip 18 an output terminal jack 19 is provided furthermore the slider 12 is provided at the outer surface thereof with a digital indicator 20 of five places consisting of seven segment indicating elements a power source switch 21 and a zero clear switch 22 further the slider 12 incorporates therein a data processing circuit 23 for detecting a magnetic variation of the magnetic scale 15 as an electrical signal when the slider 12 is moved in the longitudinal direction of the main scale 11 with the power source switch 21 being turned on indicating the measured data obtained through the process of the electrical signal in the digital indicator 20 outputting the measured data to the printer 3 through the jack 19 and the connecting cable 2 and clearing the measured data to zero when the zero clear switch 22 is operated as shown in fig2 the data processing circuit 23 comprises a detection head 31 for detecting a magnetic variation of the magnetic scale 15 as an electrical signal a detecting circuit 32 for waveform shaping an output signal from the detection head 31 to convert the same into pulse signals a counting circuit 34 for calculating the pulse signals in accordance with.