The invention is a system for improving the appearance of digital oscilloscopes' screen displays by connecting data points smoothly without gaps or jaggies.

The basic technique to overcome aliasing ("anti-aliasing") generally in use was to lessen the illumination intensity of those pixels more remote from the desired trajectory of the data points, in accordance with some formula or scheme (for example, least squares averaging).

A user of the system then makes the CRT's neck coil current proportional to I', as calculated according to the foregoing formula.

(d) means for outputting illumination intensity data as a predetermined function of the normalized vertical distance and elevation.The final decision of the PTO appellate board was that while the claim could be interpreted to describe machinery such as a combination of elements such as an arithmetic logic unit (ALU), read-only memory (ROM), and shift registers, it could also be interpreted to describe a programmed general purpose digital computer.

There were a number of procedural issues unrelated to the patentability of computer software, including whether the court had jurisdiction over the appeal.

Three judges abstained from joining any opinion on the merits, because of the jurisdictional issues, which resulted in the court's being very fractured and making it difficult to put together a majority.

[18] In the bare majority opinion for the court written by Judge Rich, the court found that Alappat claimed "a machine for converting discrete waveform data samples into anti–aliased pixel illumination intensity data to be displayed on a display means," and not an abstract idea.

Counsel for Tektronix, the successful party in the case, said that the decision held only that "digital circuitry governed by mathematical formulas can be patented."

"[20] One commentator said that two widely different interpretations were possible for what the court said the patent-eligible invention was, when it asserted that a "computer operating pursuant to software may represent patentable subject matter" if it meets the requirements of Title 35: One interpretation is that [what the court says may be patented is] some type of programmed computer equipment subsystem intertwined with an oscilloscope, in which case the scope of claim 15 is limited to an oscilloscope environment.

Or maybe meeting "all of the other requirements of Title 35" means complying with section 101 as interpreted in Benson, Flook, Diehr, Abele, Schrader and so on.

[21] The same commentator pointed out that different post-Alappat panels of the Federal Circuit had "embraced diverse interpretations of the decision.

"[23][24] Moreover, the piano roll blues theory temporarily became dominant in the Federal Circuit for about a decade after Alappat.

[26] In Bilski v. Kappos, 561 U.S. 593 (2010), the Supreme Court was unanimous that the "useful, concrete, and tangible result" test of Alappat and State Street was an incorrect statement of the law.