sensor is glued on the top side in the region of its end 17 lever 15 has a shallow depression 22 through a bore not shown in lever 15 a cable 23 is passed which connects the sensor 21 with a circuit lodged in a housing 24 housing 24 has a window 26 for a liquid crystal display further an on off switch 28 and a set screw 29 are provided at housing 24 a voltage taken off at a battery 30 and stabilized through a regulator 31 is applied at the four strain gauges 20 two resistors 32 33 bring about a reduced current consumption the voltage taken off at the sensor 21 is supplied via two resistors 34 35 to two inputs of an operational amplifier 36 which is in feedback via a resistor 37 zero point adjustment on display 27 can be carried out via a potentiometer 38 potentiometer 38 is connected with the setting screw 29 so that the zero point adjustment can be accomplished from the outside at any time the output of the operational amplifier 36 is connected to a digital voltmeter kit 39 constructed as an integrated circuit e g the icl 7106 of intersil to the voltmeter kit 39 the lcd display 27 is connected a potentiometer 40 contained in housing 24 which acts as amplification control and serves to calibrate the measuring system 14.