Where a claim in respect of a physical entity (product, apparatus) seeks to define the invention by reference to features relating to the entity's use, a lack of clarity can result. This is particularly the case where the claim not only defines the entity itself but also specifies its relationship to a second entity which is not part of the claimed entity (for example, a cylinder head for an engine, where the former is defined by features of its location in the latter). Before considering a restriction to the combination of the two entities, it should always be remembered that the applicant is normally entitled to independent protection of the first entity per se, even if it was initially defined by its relationship to the second entity. Since the first entity can often be produced and marketed independently of the second entity, it will usually be possible to obtain independent protection by wording the claims appropriately (for example, by substituting "connectable" for "connected"). If it is not possible to give a clear definition of the first entity per se, then the claim should be directed to a combination of the first and second entities (for example, "engine with a cylinder head" or "engine comprising a cylinder head").
It may also be allowable to define the dimensions and/or shape of a first entity in an independent claim by general reference to the dimensions and/or corresponding shape of a second entity which is not part of the claimed first entity but is related to it through use. This particularly applies where the size of the second entity is in some way standardised (for example, in the case of a mounting bracket for a vehicle number-plate, where the bracket frame and fixing elements are defined in relation to the outer shape of the number-plate). However, references to second entities which cannot be seen as subject to standardisation may also be sufficiently clear in cases where the skilled person would have little difficulty in inferring the resultant restriction of the scope of protection for the first entity (for example, in the case of a covering sheet for an agricultural round bale, where the length and breadth of the covering sheet and how it is folded are defined by reference to the bale's circumference, width and diameter, see T 455/92). It is neither necessary for such claims to contain the exact dimensions of the second entity, nor do they have to refer to a combination of the first and second entities. Specifying the length, width and/or height of the first entity without reference to the second would lead to an unwarranted restriction of the scope of protection.