Happy pi day! It is not a holiday that I remember from my childhood years. Nor do I remember anyone mentioning it during the first half of my career. Rapid City, South Dakota, however, where we lived for 25 years is home to South Dakota School of Mines and Technology, which is an engineering school and university students and teachers enjoyed noting March 14 as a special day. I suppose, however, that if you want to get technical, pi time would be more precise than a single day - in reality it would be an infinitely small amount of time. Lets, say, for reasons of practicality, that the actual pi time is 3.14159265358979323846264338327950288419716939937510. Of course the number goes on with plenty of numbers to the right of the decimal point. This particular number simply stops at the first zero, which seems convenient. If you were to write out pi to the millionth place beyond the decimal, you’d have to use nearly 100,000 zeros (99,959 to be precise). All of this can, I suppose be avoided by using the 16th letter of the Greek alphabet, π, instead of trying to write out the number.

In practical terms, when computing the area of a circle, there comes a point when the numbers to the right of the decimal become moot. According to Marc Rayman, Chief Engineer at the Jet Propulsion Laboratory, interplanetary navigation only requires the use of 3.141592653589793. He goes on to say that there are “no physically realistic calculations scientists ever perform for which it is necessary to include additional decimal points.” However, modern calculators and computers have a pi key that allows for extremely accurate computations. I’m fairly certain that you won’t find many slide rules in engineering universities these days. The students and professors are all using graphing calculators or even more complex portable computers to make their computations since pocket calculators became practical decades ago. A slide rule’s accuracy is dependent on size. A typical slide rule that was about a foot long could calculate accurately to 3 significant digits. I learned to operate a circular slide rule as part of my pilot training and continued to use a manual flight calculator into the early 1990’s before I obtained an electronic flight calculator. A student pilot these days would not know how to use a circular slide rule.

All of this information is essential useless for those who find pi day simply a good excuse to eat some delicious pie. I’m pretty sure that pie, savory or sweet, is the focus of the celebration for quite a few people. The love of sweet and savory treats is, when you think of it, an irrational craving. Our bodies don’t need that kind of food and people often consume too many calories when eating pie, a problem that can lead to obesity and a host of health problems. I guess that might be expected since pi is an irrational number. It cannot be expressed as the simple ratio of any two other numbers.

A traditional pie, baked in the shape of a circle, makes a good teaching tool, if one wants to garner the attention of students. Studying circles and spheres is a big deal if one is talking about exploring space, but pi is not just useful for rocket scientists. Sure, NASA scientists need to use pi to determine the size of a distant planet that can’t be actually seen, but figuring out how to fairly divide a pie among eager students, might drive home the importance of the number more quickly.

For millennia, mathematicians have invested huge amounts of time calculating the digits of pi. When calculating by hand, 500 digits is an incredible achievement. Now that computers are used, the number has been calculated to millions and even trillions. Google developer Emma Haruka Iwao might be the current record holder, having calculated pi to 31 trillion digits (31,415,926,535,897 to be exact). A few other number enthusiasts make a game out of memorizing digits of pi. My sister, when she was working on an engineering degree, managed to memorize a lot of digits, but she came nowhere near the record, which stands at 70,000 digits. I’m fairly certain I’ve never memorized anything anywhere near as long as that. After all, I only have 3.14 memorized, which is sufficient to know which day to challenge colleagues to bring a pie to a staff meeting.

I don’t even have the Greek alphabet memorized, but I do know that the 19th letter of the Greek alphabet is written as a capital T in our alphabet. That being the first letter of my name, makes it easy to remember. Tau is the name assigned to the number that is two times pi, or 6.28. Because many mathematical formulas call for 2π, tau-enthusiasts say tau would provide a more elegant and efficient way to express those formulas. I don’t know of any celebrations, even among engineers, focused on June 28th, however. I guess that there is no immediately obvious homophone for tau that inspires culinary delight. I’ve been trying to come up with some kind of word symbol for the day. However, the best I’ve come up with so far is a simple pun: “Perhaps it is time to throw in the tau and admit that pi day is more popular.” You have to admit that pie is pretty much universally enjoyed by those who get a slice whether it be March 14 or any other day. For the record, I have no objection to serving and eating pie on June 28, either.

I have been trying to use the discipline of the season of Lent to teach myself to eat more intentionally, thinking carefully about what I eat and limiting portions so that I can feel more control over my body weight. Losing a few pounds should help my health and vigor enough to make teaching myself some new tricks about eating a valuable exercise. As a result, I have no plans to consume pie today. A crunchy salad, however, is a rather poor substitute. Maybe I’ll save the salad for tau day.