Continuing with our analysis of the Greatest Design Tool ever, our objective in this article is to take a detailed look at the structure and contents of feature control frames to demonstrate that they represent “encoded” information which may only be “decoded,” not “interpreted.” With their structure defined, we will then demonstrate how to “decode” feature control frames, and in later articles how to “encode” them. In effect, this article will demonstrate that GD&T is a tool with which to research, refine, and ultimately encode the function of each feature of a part, with the objective of guaranteeing functionality and assemblability, as well as decodability for conversion into reliable manufacturing and inspection processes.

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