Durable Material: Made of carbon fiber + ABS material, it has excellent practicality.and sustainability. With locking knob: Turn the locking knob clockwise to tighten the ruler.Turn the lock knob counterclockwise to release the rule. Power button: Short press the power button to reset the zero point. Many Applications:Can be used;To measure length, angle and stroke, measure the outside angle and the inside angle.Can be used for hospitals, carpentry, building materials, school training aids, stationery/student work etc. It can professionally measure the inside and outside angle as well as the angle of objects.It can be easily closed.&a grave;any angle to provide compact and accurate measurement.It turns on automatically after 5 minutes.