A depth gauge is a precision measuring instrument, designed specifically to measure the depth of holes, recesses, cavities and distances from a plane surface to a projection. In other word, a depth gauge is a variation of the ruler. The depth gauge consists of a ruler—usually a narrow one to measure the depth of holes, counter bores, etc. There is a base through which the ruler can slide up and down, and a locking screw on the cover to clamp the ruler in place. The base, which is machined flat and at right angles to the ruler, is placed on a reference surface and the ruler lowered into the hole or recess until its bottoms. Keep in mind avoid touching any of the measuring surfaces of both the subject being measured and the digital depth gauge with bare hands as it may cause inaccuracy due to the sweat on your hands (if you don’t wear the gloves while measuring). Keep them clean and dry all the times.