It may be problematic to have claim features that are defined by an object that is outside the claim. The Guidelines (C-III 4.14) have something to say on this topic:
“… 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. …”
The present decision shows a case where such a reference to the dimensions of a second entity was found not to be allowable.
Claim 1 (of the first auxiliary request) before the Examining Division (ED) read:
Root canal reamer for use in handpieces, having a reaming section with two or more cutting blades (L) with progressively increasing diameter and constant taper angle, characterized in that the length of said reaming section is such that, when said root canal reamer is inserted in the root canal until the apex, at least a part of said reaming section is effective on the apical portion of said root canal and at least a further part of the same reaming section is simultaneously effective on the coronal portion of said root canal, wherein the length (A) of the reaming section comes between 16 and 30 mm.
The ED refused this request inter alia for lack of clarity:
“… The applicant also amended the characterizing portion of claim 1 in an attempt to define the subject matter of the invention with respect to a second, unclaimed entity, namely human teeth. The length of the reaming section has been made dependent on the size of the human tooth because it is claimed that the length must be such that “said reaming section is effective on the apical portion of said root canal and at least a further part of the same reaming section is simultaneously effective on the coronal portion of said root canal”. Teeth are not considered to be standardized entities nor are they of equal size, since they Vary within the mouth of the patient from the incisors to the molars. Chipping or breaking of teeth provides for even more variability in the dimensions of teeth, as does the difference between baby teeth and adult teeth and between healthy and unhealthy teeth. It is not possible to infer clearly from this part of claim 1 what technical features, if any, can be understood and used as a way to delimit the scope of the invention. …”
The applicant filed an appeal as well as a new set of claims, claim 1 of which read:
Root canal reamer for use in handpieces, having an apical reaming portion and a coronal reaming portion with at least two cutting blades (L) and with progressively increasing diameter and constant taper angle, the cutting blades (L) covering both the apical portion and the coronal portion, wherein the whole reaming length (A) exceeds the ISO standard length of 16 mm and reaches a maximum length of 30 mm.
The Board agreed with the ED that there was a lack of clarity:
 The decision under appeal found that claim 1 of the first auxiliary request lacked clarity because it defined a reamer on the basis of the apical and coronal portion of the human tooth […].
The new claim 1 still defines the reamer as having an apical and a coronal portion (with at least two cutting blades covering both the apical and the coronal portion). That is the definition of the reamer is still dependent on the apical and the coronal portion of the human tooth.
The objection of the first instance of lack of clarity was correctly reasoned since it is not possible to clearly define a reamer on the basis of the human tooth, being the size of the human tooth extremely variable and depending on the age of the subject, the type of the tooth (incisive, canine, molar) and the health of the tooth itself, as clearly stated in the decision under appeal.
The appellant in its statement of grounds addresses the objection of lack of clarity with the sole sentence:
“A set of new claims is submitted, claim 1 of which defines the features of the invention in a clearer manner”.
The appellant did not bring forward any new argument or fact which could lead to a different founding on this issue.
Therefore the objection of lack of clarity raised by the first instance has to be confirmed.