4.17 References to the description or drawings 

As indicated in Rule 43(6), the claims must not, in respect of the technical features of the invention, rely on references to the description or drawings "except where absolutely necessary". In particular, they must not normally rely on such references as "as described in part ... of the description" or "as illustrated in Figure 2 of the drawings".

The emphatic wording of the excepting clause is important to note. The onus is on the applicant to show that it is "absolutely necessary" to rely on references to the description or drawings in appropriate cases (see T 150/82).

An example of an allowable exception is an invention involving a peculiar shape that is illustrated in the drawings but cannot be readily defined either in words or by a simple mathematical formula. Another special case is where the invention relates to chemical products, some of whose features can be defined only by means of graphs or diagrams.