A dial indicator is a precision measuring tool used to measure small distances or variations in height. It features a dial with a needle that moves in response to a plunger, which contacts the surface being measured. The dial displays the measurement in either inches or millimeters, allowing for accurate readings of up to 0.001 inches or 0.01 millimeters. These instruments are commonly used in machining and engineering to check the alignment of parts, the flatness of surfaces, or the roundness of objects. They are essential for quality control in manufacturing processes and are often used alongside other tools like calipers and micrometers.