Digital Ruler & Protractor: A ruler with digital protractor function, able to measure length as well as angle at the same time. Say goodbye to complicated measuring or plotting work. Metric and Imperial System: Length measurement range 0 to 280 mm (the 2 rulers all measure 7 inches). Angle measuring 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 / unlock the ruler at any angle, to avoid shifting or losing the measured angle. Simple but Durable: Simple design, but made of stainless steel, an excellent material ensuring exceptional strength. The lifespan of the button battery is over 2000 hours to solve any battery concerns.