In 2009, the US House of Representatives agreed to a resolution designating March 14 as “Pi Day”.
So I thought I’d see whether I could rustle up a nice example of pi in the Code of Federal Regulations. I did manage to find the π I was looking for, but it turns out that pi also gives us some examples of why we need to disambiguate.
In the process I also found:
- Pi Tape® (who knew?) in the dynamometer verification and calibration procedures in vehicle emissions tests;
- The specific heat of water: “Cpi = the specific heat of the water of the ith draw” in the test methods for measuring the energy consumption of water heaters;
- Required credentials for a principal investigator applying for a permit to study a wreck under the control of the Navy;
- The post-inoculation requirements of the chicken embryo test for avian encephalomyelitis vaccine inactivation;
- Packaging instructions requirements for transporting explosives;
- Tax treatment of passive income;
- A mailing address in the Philippine Islands.
So the story of “pi” in the CFR is a story of disambiguation. When we read (or our software parses) the original text of a particular regulation, it’s reasonably straightforward to tell which of the many “pi”s it’s discussing. We have capitalization, punctuation, formatting, and structural and contextual clues. Once the search engines work their case-folding, acronym normalization, and other magic, we end up with an awful lot of “pi”s and very little context.
Postscript. The real pi was a bit of a letdown: “P = pi (3.14)” – well, close enough.
