No two parts can be produced with identical measurements by any manufacturing process. In any production process, regardless of how well it is designed or how carefully it is maintained, a certain amount of natural variability will always exist. The designer has to suggest these tolerance limits, which are acceptable for each of the dimensions used to define shape and form, and ensure satisfactory operation in service. Before an object can be built, complete information about both the size and shape of the object must be available. The exact shape of an object is communicated through orthographic drawings, which are developed following standard drawing practices. The process of adding size information to a drawing is known as dimensioning the drawing. Geometrics is the science of specifying and tolerancing the shapes and locations of features on objects. Once the shape of a part is defined with an orthographic drawings, the size information is added also in the form of dimensions. Dimensioning a drawing also identifies the tolerance (or accuracy) required for each dimension. If a part is dimensioned properly, then the intent of the designer is clear to both the person making the part and the inspector checking the part. A fully defined part has three elements: graphics, dimensions, and words (notes). A well dimensioned part will communicate the size and location requirements for each feature. Communications is the fundamental purpose of dimensions.  Parts are dimensioned based on two criteria:  Basic size and locations of the features.  Details of a part's construction and for manufacturing.