Gear Tooth vernier calipers

Gear Tooth vernier calipers is designed to measure in .001″or 0.02mm the thickness of gear teeth at the pitch line (the chordal thickness of the teeth) using the distance from the top of a tooth to the chord. For the same purpose, it can also be used for measuring hobs, from and thread tools,etc.
The thickness of a tooth at the pitch line is measured by an adjustable tongue. Each of these is adjusted independently by screws on the graduated bars.
For tool operation:
a. Furnished with the tool, the number of teeth of the gear in question, and find the corrected addendum(s�?. This figure is for one diametral pitch for inch measure, so multiply it by the required moduel number. This gives a corrected addendum for this particular number of teeth.
b. Next, measure the actual outside diameter of the gear and add or subtract one-half the diffence between the theoretical gear diameter and actual measured gear diameter from corrected addendum(s�? found in the first step.
c. Set the new calculated addendum figure on the adjustable tong of the tool.
d. Now, with the tongue on the top of the tooth, measure the chordal thickness with the horizontal vernier jaw and compare with the figure in the “t�?.
e. All inch graduations are read to .001�?