Digital protractor ruler: A ruler with the function of digital protractor, able to measure the length as well as the angle at the same time. Say goodbye to complicated measuring or plotting work. Metric and Imperial System: Length measurement range 0 to 400 mm (the 2 rulers are all 7 inches). Angle measurement range 000.0 to 999.9, the ruler can be rotated more than 2 turns. Resolution 0.1; accuracy 0.3. Zero at any position (taring): Press the small zero button for one second, the value on the angle screen will be reset to zero and you can start the measurement at any angle. Turn the large knob in the center to lock and unlock the ruler at any angle, to avoid any movement or loss of the measured angle. Simple but durable: Simple design, but in stainless steel, an excellent material ensuring exceptional solidity. The button battery life is more than 2000 hours to solve any battery life concerns.