4-in-1 Multifunction High Precision 360 Degree Digital Angle Finder Protractor Level Finder Scales Ruler Our eyes are not as accurate as the machine and there are always some errors in the readings. Friendly Tips: 1.The button is not used for locking. The knob can only be loosened or tightened according to the user's usage habits and needs.Tightening can't completely fix the angle, just avoid moving the digital angle ruler when drawing a line, which makes the measurement more convenient and reliable. 2. If you want to "reserve" the angle value you need, you must use the data hold function. You must press the red HOLD button instead of turning the knob to lock. 3.It can be used as a spirit level, helping you to check and calibrate (NOTE: this is NOT a digital level, will not show the number on the LCD, will only help you to judge whether it is horizontal/vertical/the horizontal plane is tilted or not) 4. The LCD screen is flickering or the digital display is incomplete, it means the