A depth gauge device including a body extending a central longitudinal axis and including a channel and a light-passing hole, the light passing hole open to the channel, a light source mounted in the body for generating a light beam, the light beam passing through the light- passing hole toward a surface of a drill-bit extending through the channel, the light beam forming an incident light beam when reflected away from the drill-bit surface, an image sensor mounted in the body for sensing the incident light beam and generating a plurality of successive images of the drill-bit surface to detect variations in the position of the drill-bit moving through the channel and an clamp coupled to the body, the clamp including a plurality of adjustable arms configured to clamp the device to a protection sleeve.
