Section 112 of the Patent statute requires claims to be definite. Patent Office examiners in the US often reject claims that use the term "about" as being indefinite. Here, United Technologies appealed the rejection of a gas turbine buffer system. Claim 17 included the limitation of "a bypass ratio of greater than about six (6)," claim 18 included the limitation of "a low Fan Pressure Ratio of less than about 1.45," and claim 19 included the limitation of "a pressure ratio that is greater than about 5.
There is nothing inherently wrong with using the term "about" in a claim, as long as it is done properly and the claim scope is clear. United Technologies made this exact point, arguing that variable claim terms are not necessarily indefinite and that it is conventional in engineering to have an implied tolerance based upon the number of decimal places used, citing MPEP §2173.05(b). In other words, because different claim terms used different decimal places, this means that the range of how close a value was to the claimed number could be ascertained by a person skilled in the art.
The PTAB flipped this argument around and used it as a reason to affirm the Examiner. The PTAB explained that although they agree that the term "about" is not necessarily always indefinite, the Appellants offered no evidence or persuasive technical reasoning to explain what tolerances are implied by the term "about" as recited in the claims. Further, the PTAB found that because different claims used different decimal places, the term "about" recited in claims 17 and 19 could have a different meaning than the same term recited in claim 18, thereby creating confusion regarding the scope of the term. Ouch. While this hyper-technical point may be true, it is hard to understand how the combination of elements having different meanings is a problem when they are in different claims.
The takeaway practice tip here is to be extremely careful in using terms such as "about" in the claims, and to ensure that the use is consistent and fully explained in the specification.