Process and apparatus for wrench capable of displaying torque value

The present invention is torque displaying method and device for wrench. Based on that the resistance of material is proportional directly with length and proportional inversely with area, resistance variances are converted in a Wheatstone bridge into output voltage and the voltage is converted via amplifier, data processor, etc. into digital signal and displayed via output unit to express the torque. The resistance inside the wrench is measured with tension gage with known resistance, piezoelectric crystal and other sensing element, and the tension gage is connected to an integrated element to display the torque number or a buzzer to tell the torque value.