The area defined by the claims must be as precise as the invention allows. As a general rule, claims which attempt to define the invention by a result to be achieved are not allowed, in particular if they only amount to claiming the underlying technical problem. However, they may be allowed if the invention either can only be defined in such terms or cannot otherwise be defined more precisely without unduly restricting the scope of the claims and if the result is one which can be directly and positively verified by tests or procedures adequately specified in the description or known to the person skilled in the art and which do not require undue experimentation (see T 68/85). For example, the invention may relate to an ashtray in which a smouldering cigarette end will be automatically extinguished due to the shape and relative dimensions of the ashtray. The latter may vary considerably in a manner difficult to define whilst still providing the desired effect. So long as the claim specifies the construction and shape of the ashtray as clearly as possible, it may define the relative dimensions by reference to the result to be achieved, provided that the specification includes adequate directions to enable the skilled person to determine the required dimensions by routine test procedures (see F‑III, 1 to F‑III, 3).

However, these cases have to be distinguished from those in which the product is defined by the result to be achieved and the result amounts in essence to the problem underlying the application. It is established case law that an independent claim must indicate all the essential features of the object of the invention in order to comply with the requirements of Art. 84 (see G 2/88, Reasons 2.5, and G 1/04, Reasons 6.2). Art. 84 also reflects the general legal principle that the extent of monopoly conferred by a patent, as defined in the claims, must correspond to the technical contribution to the art. It must not extend to subject-matter which, after reading the description, would still not be at the disposal of the person skilled in the art (T 409/91, Reasons 3.3). The technical contribution of a patent resides in the combination of features which solve the problem underlying the application. Therefore, if the independent claim defines the product by a result to be achieved and the result amounts in essence to the problem underlying the application, that claim must state the essential features necessary to achieve the result claimed (T 809/12, Reasons 2.6-2.9.2), see also F‑IV, 4.5.

The above-mentioned requirements for allowing a definition of subject-matter in terms of a result to be achieved differ from those for allowing a definition of subject-matter in terms of functional features (see F‑IV, 4.22, and F‑IV, 6.5).