GDTP stands for Geometric Dimensioning and Tolerancing Professional. It is a certification program offered by the American Society of Mechanical Engineers (ASME) that verifies an individual's competence in understanding and applying the principles of Geometric Dimensioning and Tolerancing (GD&T). GD&T is an essential language used for clear communication in manufacturing, ensuring that designs are manufactured as intended. ASME's Y14.5 Standard serves as the authoritative guideline for GD&T, and GDTP certification is based on either the 1994 or 2009 revisions of this standard, including its appendices and the application of its principles and practices. The certification program offers two levels of certification: Technologist and Senior.  This section is based on Chapter 2 of ASME STD. In this section, topics covered GENERAL TOLERANCING AND RELATED PRINCIPLES, AND FORMER PRACTICES  including

(a) application of tolerances (b) tolerance expression (c) interpretation of limits (d) plated and coated parts (e) single limits (f) tolerance accumulation (g) limits of size (h) relationship between features (i) applicability of RFS, MMC, LMC (j) virtual/resultant condition (k) geometric tolerance application to gears and splines  (l) screw threads (m) datum features at virtual condition (n) angular surfaces (o) conical tapers,(p) flat tapers (q) radii (r) statistical tolerancing identification (s) former practices (ASME Y14.5M-1994, Appendix D)