The description, the claims and the abstract may contain chemical or mathematical formulae. Such formulae may be written by hand or drawn if necessary but it is recommended that appropriate drafting aids or materials, such as stencils or transfers, be used. For practical reasons formulae may be grouped together on one or more sheets in the description and paginated with it. In such cases, it is recommended that each formula be designated by a reference sign and that the description contain references to the formulae whenever necessary.[R. 11.9(b); 11.10(b); ]

Chemical or mathematical formulae must employ symbols in general use and must be drawn in such a way that they are completely unambiguous. Numerals, letters and signs which are not typed must be legible and identical in form in the various formulae, irrespective of the element of the international application in which they appear. Chemical or mathematical formulae appearing in the text of the international application must have symbols, the capital letters of which are at least 0.28 cm high. Where they appear on sheets of drawings, these symbols must be at least 0.32 cm high. All mathematical symbols used in a formula which appear in the description or on sheets of drawings should be explained in the description, unless their significance is clear from the context. In any case, the mathematical symbols used may be collated in a list.[R. 11.9(d); ]