On April 27 2015 the Federal Circuit issued a decision in Biosig Instruments v Nautilus Inc, on remand from the Supreme Court. Applying the Supreme Court's new 'reasonable certainty' standard for indefiniteness, the Federal Circuit again found the claims not indefinite.


Biosig sued Nautilus for infringing US Patent 5,337,753 (the '753 patent), which was directed to a heart rate monitor for exercising. On summary judgment, the district court found the '753 patent invalid as indefinite. The Federal Circuit reversed under its previously applied test that a claim was indefinite only when it was "not amenable to construction" or "insolubly ambiguous".(1)

The claim term asserted to be indefinite was a spaced relationship, which the Federal Circuit described as the distance on a user's body between the live and common electrodes that sense heart rate. The Supreme Court rejected the 'insolubly ambiguous' test, vacating and remanding the decision. The Supreme Court held that the proper test for indefiniteness is when "claims, read in light of the specification delineating the patent, and the prosecution history, fail to inform, with reasonable certainty those skilled in the art about the scope of the invention".(2)


Applying the new standard, the Federal Circuit concluded that Biosig's claims "inform[ed] those skilled in the art with reasonable certainty about the scope of the invention". The Federal Circuit relied only on intrinsic evidence (ie, the specification, claims, figures and prosecution history), reviewing the claim scope determination de novo under Teva Pharm USA Inc v Sandoz Inc.(3)

In analysing whether the spaced relationship was indefinite under the new standard, the Federal Circuit noted that the judiciary commonly applies reasonable certainty in a wide variety of cases. The court then looked to prior case law where context had determined whether terms of degree and functional language were definite. The court noted that terms of degree had been definite where appropriate standards for measurement were either taught by the specification or within the knowledge of those skilled in the art before the invention. Embodiments in the specification had also rendered claims definite by teaching "objective boundaries". However, a term of degree had been indefinite when it depended on the "unpredictable vagaries of any one person's opinion".

Although the '753 patent did not define the spaced relationship with actual parameters, the Federal Circuit found that the claim language, specification, figures and prosecution history sufficiently defined the bounds of the spaced relationship between the live and common electrodes. This intrinsic evidence taught that the distance between the live and common electrodes could not be greater than the width of a user's hand, and could not be so small as to be effectively only one detection point (effectively merging the separate electrodes into one), in addition to teaching ways to measure the appropriate distance.

The Federal Circuit therefore concluded that the claimed spaced relationship informed those skilled in the art of the scope of the invention with reasonable certainty, in compliance with 35 USC § 112, paragraph 2. Thus, despite the change in law, the court reached the same conclusion it had made under the 'insolubly ambiguous' standard applied before the remand from the Supreme Court. The Federal Circuit accordingly reversed the finding of indefiniteness and remanded the case back to the district court.

For further information on this topic please contact Joshua I Rothman at Fitzpatrick, Cella, Harper & Scinto by telephone (+1 212 218 2100) or email (jrothman@fchs.com). The Fitzpatrick, Cella, Harper & Scinto website can be accessed at www.fitzpatrickcella.com.


(1) Biosig Instruments v Nautilus Inc, 715 F3d 891, 898 (Fed Cir 2005).

(2) Nautilus Inc v Biosig Instruments Inc 134 SCt 2120, 2124 (2014).

(3) 135 SCt 831, 842 (2015).

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