Federal Circuit says Basic Math ≠ Modification

Blackbird v Fitbit


Blackbird Tech owns US patent number 6,434,212 directed to a device that counts an individual’s steps.  Based on the length and rate of those steps, the device provides information such as distance traveled and speed.  Fitbit and Wahoo Fitness each sought an inter partes review of claims 2,5 and 6.  PTAB instituted the requested reviews and consolidated the proceedings.  The Board determined that Fitbit had proven claim 6 of the ‘212 patent unpatentable for obviousness.  Blackbird appealed.

Claim 6 states in pertinent part:

A data processor programmed to calculate a distance traveled by multiplying a number of steps counted by a stride length that varies according to a rate at which steps are taken, and further programmed to derive an actual stride length from a range of stride lengths calculated from a range of corresponding stride rates.

The device described in the ‘212 patent thus purports to improve accuracy in calculating the figures of interest, such as distance or speed.

The appeal

Blackbird limited their appeal to arguing that the Board erred in finding that one of the cited pieces of art, Kato, disclosed the above limitation of claim 6.  Kato, in turn, discloses the following equation for determining a walking speed:

SP = ST x PI

Where SP is the walking speed, ST is stride length, and PI is “pitch, expressed as number of steps every 10 seconds.”  The distance travelled by the walker is then calculated by multiplying the walking speed by the time spent walking.  And so, the Board determined, Kato in essence taught the following equation:

Distance = (ST x PI) x Time

Which can be further reduced to

Distance = stride length x number of steps.


The Federal Circuit agreed with the Board:

Substantial evidence supports the Board’s finding that a relevant skilled artisan would read Kato as teaching a data processor programmed to calculate a distance traveled by multiplying the number of steps counted by a stride rate length.

Blackbird argued that the Board was obligated to explain why a relevant skilled artisan would have taken the steps of expressing pitch as “steps/time” and cancelling out the numerator-time with the denominator time.  According to Blackbird, the Board “worked backward, with knowledge of the claimed invention, to modify the Kato reference in such a way as to arrive at the claimed invention.”

The Federal Circuit disagreed:

But the Board’s conclusion of unpatentability did not rely on a modification of Kato’s equation – it relied on a finding that a relevant skilled artisan would consider Kato’s equation to teach claim 6’s limitation.  The Board could readily find that … [a skilled artisan] would understand Kato’s teaching of a very simple multiplicative relationship to teach the form of that relationship that involves the elementary process of unit cancellation between numerator and denominator.  Accordingly, the Board had a sufficient basis to find that a relevant artisan would have considered Kato’s method for calculating distance traveled to be identical to claim 6’s limitation.