For Tubing and Casing, properly setting a TH-3002R thread height gage is easy, yet often done incorrectly. The setting standard (1014) has a square-shaped notch and a v-shaped notch.
First, use the square-shaped notch, zero the gage. Then, use the v-shaped notch to verify the gage is zeroed. If the gage does not read zero on the v-notch, most likely, the self-centering contact point needs to be replaced.