If you take a depth gage add a vernier , then you get a vernier depth gage.We can justify using a fairly unreliable instrument, such as a vernier caliper, because it provides a wide range inexpensively . However, depth micrometers beat vernier depth gages in terms of centimeters per dollar and reliability per dollar. The important point we need to learn about vernier depth gages, as well as depth micrometers , is that they conform with Abbeâ€™law.The vernier depth gage differs slightly from the vernier caliper and the caliper and the caliper height gage in that the vernier slide assembly remains fixed while the steel rule is moved to obtain that is held on the work by one hand while the blade is operated with the other.Operating on the principles of vernier caliper gages, vernier depth gages differ in the design application of the basic concept , resulting in the reversal of the usual process:
1. The slide is connected with the cross beam of the instrument , which , by contacting a reference plane on the object surface , establishes the datum of the measurement.
2. The end face of the beam takes over the function of the movable jaw, in contacting the object element whose distance from the datum is to be measured.
The use of the vernier depth gage is not limited to actual depth measurements , although these constitute the major application for the instrument. Distances that are referenced from and are normal to a flat surface of the object , can also be measured conveniently with the aid of vernier depth gages. An example of this latter type of use is measuring the coordinate distances of toolmaker buttons in relation to the edges of a rectangular workpiece.