1. Dimensional checking.
2. Position checking.
When we are talking about position checking it is a size of a feature. When we are talking about position checking then it is a relative. In GD&T we are consisting both with tolerance. GD&T is symbolinc language which is understood by Symbols.
Following is an example for GD&T
GD&T give you a perfect imaginary world in which you can find Tolerance Zone, tolerance value, Datum?s, Coordinate Systems and Basic Dimensions. Which all are restricted by the limits on the imperfect form, size, orientation and location of real world, GD&T correlate machine part Features (e.g. planar surfaces, bores and shafts) and their Components (surface points, axes, mid-planes). Figure 1/2 above illustrates a partially GD&T encoded object, Figure 22 below illustrates the resulting collection of Tolerance Zones and the controlling Datum Reference Frame (DRF) whose axes are labeled.