A working knowledge of geometric dimensioning and tolerancing (GD&T) is necessary if engineers want to truly understand the designer's intent, and therefore plan accurate and appropriate inspection of the product the drawing represents. As part tolerances get tighter and tighter, it's more important than ever to establish a realistic, agreed-upon part drawing that subsequent inspections can be measured against.
GD&T is a precise mathematical language that describes the size, form, orientation and location of part features. It's also a design-dimensioning philosophy that encourages designers to define a part based on how it functions in the final product.