Descriptions of Dimensions and Symbols – General section 21003.1/.2, from the SAAMI Technical Manual (Centerfire Rifle) which defines “basic” and “reference” and other terminology that is consistent with the International Geometric Dimensioning and Tolerancing (GDT) drawing protocols. Section 21003.3 defines SAAMI dimensioning protocol and process relevant to cartridge and chamber drawings as found in the ANSI affirmed SAAMI National Standards. Section 21004.1/.2/.3/.4 Description of Dimensions and Symbols - Centerfire Rifle will give you a practical graphical presentation of the application of the dimensioning protocol. I believe that you will find this very beneficial in understanding the SAAMI TDCC drawing protocol.