This 6 inch electronic digital caliper has manual power on and off so it won't go off and lose your measurement. There are three buttons. One turns on the power and sets the readout to zero. The second switches between inch and metric display. The third button turns the power on and off. You can make absolute or relative inside, outside, depth, and step measurements and it can be set to zero at any position. The caliper comes in a nice fitted storage case.