Overall dimensions When a length consists of a number of dimensions, an overall dimension may be shown outside the dimensions concerned(see Fig. 1.10) The end projection lines are extended to allow this. When an overall dimension is shown, however, one or more of the dimensions which make up the overall length is omitted. This is done to allow for variations in sizes which may occur during production. The omitted dimension is always a non-functional dimension, that which does not affect the function of the product. Functional dimensions are those which are necessary for the operation of the product, dimensions are essential.