About is one of the great weasel words of patent claim drafting.  Few things look as dangerous to a patent drafter as the sharp edge of a numerical limitation without the blunting influence of “about.”  “About” has been used in the claims of about 22% of utility patents issuing since 1976.  While it is frequently employed by drafters, often not much care is taken in properly defining its boundaries.  In Ferring B.V. v. Watson Laboratories, Inc. – Florida, [2014-1377] (Fed. Cir. 2014), the determination of infringement turned on the meaning of “about” in the phrase “less than about 70%”.  Ferring argued that about meant +/- 10%, based upon some language in a test referenced in the claim language, so that less than about 70% actually meant less than 63% to 77%.  Apotex meanwhile argued that it meant +/- 5%, so that about 70% actually meant less than 66.5 to 73.5%, which did not encompass the less than 75% of Apotex’s product.  In the absence of any defintion in the patent, the Federal Circuit declined to place a numerical limitation on “about,” instead giving about its ordianry meaning:

“About” is not defined either explicitly or by implication by the specification. We think that the district court did not err in giving the term “about” its ordinary meaning and in refusing to give it a more specific construction. See also Merck & Co., Inc. v. Teva Pharms. USA, Inc., 395 F.3d 1364, 1369–70 (Fed. Cir. 2005) (the term “about” should be given its ordinary and accepted meaning of “approximately” unless the patentee clearly redefines “about” in the specification). We affirm the district court’s construction of “about” to mean “approximately,” as well as its refusal to construe “about” to represent a particular numerical error rate.

“About” is a often used and time honored weasel word, but to be used to best effect, some standard should be provided for determining its effect on the so-modified claim element.
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