A digital depth gauge apparatus is provided for measuring a depth of a hole in, or surface of, an object using a variable-resistance sensor. The apparatus comprises an elongated reader body that includes a distal end and a proximal end having a longitudinal axis and a user interface including a display and at least one actuator that controls operation of at least one of the display and the apparatus. The apparatus includes a probe that extends from the distal end of the reader body, the probe including a tip for locating a distal surface of the object. The reader body proximal end is configured to abut an other surface of the object. An electrical resistance-based sensor is provided to determine an extension distance of the probe from the body.