Editing Engineering drawing (section)

== Systems of dimensioning and tolerancing ==

Almost all engineering drawings (except perhaps reference-only views or initial sketches) communicate not only geometry (shape and location) but also dimensions and [[engineering tolerance|tolerances]]<ref name=":0" /> for those characteristics. Several systems of dimensioning and tolerancing have evolved. The simplest dimensioning system just specifies distances between points (such as an object's length or width, or hole center locations). Since the advent of well-developed [[interchangeable parts|interchangeable manufacture]], these distances have been accompanied by tolerances of the plus-or-minus or min-and-max-limit types. ''Coordinate dimensioning'' involves defining all points, lines, planes, and profiles in terms of Cartesian coordinates, with a common origin. Coordinate dimensioning was the sole best option until the post-World War II era saw the development of [[geometric dimensioning and tolerancing]] (GD&T), which departs from the limitations of coordinate dimensioning (e.g., rectangular-only tolerance zones, tolerance stacking) to allow the most logical tolerancing of both geometry and dimensions (that is, both form [shapes/locations] and sizes).

[[File:Technical_drawing,_1891.jpg|Technical drawing, 1891|440x440px]]