In mass-production industries, it has been realized that Product Design (PD) departments and Manufacturing Engineering (ME) departments under the same organization show quite different interests in the same product line.
While John Goodman and Arnold Schwarzenegger are both 6’2”, few would argue that they have similar body shapes. What this says, simply, is that measuring size does not necessarily say anything about shape.
What is GD&T? GD&T, namely “Geometric Dimensioning & Tolerancing,” is a symbolic language with which to 1) research, 2) refine and 3) ultimately “encode” the functions of each feature of a machine part by specifying permissible limits of imperfection.
Manufacturers of complex component parts understand all too well how important it is to acquire an accurate and precise scale of measurement to check their parts to specification and establish conformity with the data.
GD&T is difficult to get right even though it is very logical. What does “right” mean? Right means several things, but mainly that it imposes achievable, fully function based and only necessary permissible limits of imperfection using absolutely syntactically correct code.