A flatness gage is a digital dial indicator type instrument used to measure lap plate flatness. It consists of a gauge body with two contact feet at one end and one vertically adjustable foot at the opposite end that can be adjustable from 100 mm to 250 mm. These three points serve as the reference plane (geometry defines a plane by three points) and a vertical stylus dial indicator measures the lap plates positive or negative deviation from the reference plane. This instrument is very convenient to use and provides a measurement value via the dial indicator. The resolution of the indicator is 1 micron.