### State of the Tau 2016

Happy Tau Day, everyone! It’s hard to believe it’s already been six years since The Tau Manifesto launched and the real battle against pi’s supremacy began.

I don’t keep careful statistics, but I can confidently state that awareness of tau is enormously widespread. As an active member of the Caltech alumni community, for example, I frequently meet Caltech undergraduates, and they’ve virtually always heard of Tau Day.

Similarly, I’ve found in the programmer community that a fair fraction have heard of tau. In my own little corner of tech, every so often someone will freak out upon realizing that the author of the Ruby on Rails Tutorial and The Tau Manifesto are the same person. Indeed, today I hope to blow more than a few such minds, because I’ve just launched the new edition of the Ruby on Rails Tutorial book—on Tau Day!

One cool thing is seeing people wearing the Official Tau Shirt, which as usual is available for a limited time (sales expire tomorrow). For example, my mother reported seeing one on an elementary school student in Orange County, California, last year. And just a couple of weeks ago I was driving through downtown Los Angeles when I saw a woman wearing a Tau Shirt. I recognized her as my friend Carol Hoffstedt, so I rolled down the window and said, “Hey, Carol! You win!” I mean, what are the odds!?

As in previous years, people continue to amaze me with the incredible variety of creative projects inspired by tau. For example, an alert tauist passed along this remarkable Tau Day Sonnet, written for Tau Day last year:

As a big fan of the sonnet form myself, I can hardly imagine a better Tau Day present than this. Well, maybe beer (see below).

A second tauist, this one at MIT, told me about a “Tau Day Hack” involving “Tau on the Cow” (don’t ask me exactly what it means!):

I’m glad to see MIT picking up the tau ball and running with it—and challenge my fellow Techers at Caltech to do the same. (Hint, hint!)

Finally, the ever-enthusiastic Joseph Lindenberg passed along this fantastic bit of tau culture found in a most unexpected place: a specialty beer from Hawkshead Brewery called Key Lime Tau!

The [Key Lime Tau] beer, originally a collaboration brew with Crooked Stave (USA), is our take on a key lime pie. It was brewed on both sides of the Atlantic, hence two ‘pies’ and is 6.28% in strength.

6.28% in strength! How can you not love that?!

Alas, it looks like Key Lime Tau beer is pretty hard to come by, and I haven’t yet procured any for myself, but for next year I’ll do my best to fulfill the promise implicit in this lovely poster, and drink Hawkshead Key Lime Tau on International Tau Day!

Until next year—Happy Tau Day!

Michael Hartl
Founder, Tau Day
Author, The Tau Manifesto

### State of the Tau 2015

Happy Tau Day 2015! Interest in the true circle constant (τ = C/r = 6.283185…) and The Tau Manifesto continued unabated this year, highlighted by a surge of attention on the “Pi [Half Tau] Day of the Century” (3/14/15). (Tau will have its revenge on 6/28/31—party at my place!) As one of the leaders of the “opposition”, I was invited to the Pi Day festivities at the Exploratorium in San Francisco—the organization that originally created Pi Day—but I was on vacation in Barcelona at the time and was unable to attend. (I know, rough life!) That the invitation was proffered in the first place is an excellent sign, though, as it serves as proof that even the Paladins of Pi recognize tau as a legitimate rival.

Here are some of the highlights since last year’s Tau Day:

• I gave a well-received 15-minute talk at the BIL Conference (Los Angeles regional). BIL was founded as a sort of counter-conference to TED, and it was my pleasure to have the opportunity to prepare a condensed version of the original Tau Talk suitable for a general audience.

• Inspired by feedback from the BIL talk, I’ve updated The Tau Manifesto with some new material, including added emphasis on an important observation: while there are infinitely many two-dimensional shapes with constant diameter, there is only one (the circle) with constant radius.

• In case you missed it, tau/2 at Google evaluates to 3.14159… This got a big ovation at the BIL Conference talk!

• In advance of Half Tau Day, Taylor University hosted the Indiana Mathematical Association of America Spring Section meeting, which featured the Great Tau/Pi Debate of 2015. Check it out, and decide for yourself who makes the better argument!

• Robin Whitty continued to use tau freely in on his site Theorem of the Day. In fact, he’s concluded that tau is now well-known enough among his readers that it doesn’t require additional explanation, writing that “Four out of the last 10 theorems I’ve posted at theoremoftheday.org have featured tau and I’ve now given up adding (=2pi) on the assumption that everyone should know by now!”

• Joseph Thiebes has created some tau-inspired merchandise at Tau Stuff, featuring several different tau pendant designs.

• To improve his trigonometry course, mathematics teacher Phil Smith modified a couple of open-source math textbooks to use tau, and has posted the results online at Tau for Trigonometry. Thanks, Phil!

• Jose Luis Garcia del Castillo from Fathom Information Design reports on the success of a second “tau fiesta” called ¡FiesTau!, which involved the “whole office playing Taupardy!, our own Jeopardy-inspired Tau quiz game written in Processing [a programming language that supports tau].” They’ve even released the source of Taupardy!, so now anyone can play! Fathom Information Design is also the maker of Peep in Tau, an app that lets you search for a number of your choice in the digits of tau.

• Joseph Lindenberg shares an analogy he’s found useful in explaining tau to the uninitiated:

Using tau instead of pi makes math clearer, and thus easier to understand.

Using pi is like having a weird car whose odometer and speedometer display half-miles and half-miles-per-hour, while all the road signs show miles and miles-per-hour.

(The road signs of math are naturally in units of tau.)

So you constantly have to convert between what your car says and what the road signs say. 55 mile-per-hour speed limit? Make sure your speedometer needle doesn’t go over 110. But instead of nice round numbers like 55, imagine the sign says 68.7 miles-per-hour. So your speedometer needle shouldn’t go above… how much? Your trip odometer reads 35.7. So you’ve traveled… how many miles?

Sometimes you must multiply by 2. Sometimes you must divide by 2. And before doing either, you must always stop and decide which to do in this particular case. If you’re driving in heavy traffic, or bad weather, or you’re lost, you don’t want that distraction. The same is true if you’re lost while trying to learn trigonometry.

Thanks for all the support! For me, that makes for a very happy Tau Day.

Michael Hartl
Founder, Tau Day
Author, The Tau Manifesto

### State of the Tau 2014

Happy Tau Day, everyone! This was a huge year for $\tau$, with continued adoption in programming languages and classrooms, appearances in a couple of prominent webcomics (xkcd & SMBC), and a big endorsement from Google. I also received an amazing parable about pi and tau from a precocious high-school student—seriously, give it a read.

Here’s a list of some of the highlights since Tau Day 2013:

I’ve been gratified by the continued enthusiasm for $\tau$ since the launch of The Tau Manifesto in 2010. I especially appreciate the support of Robert Palais, Joseph Lindenberg, Peter Harremoës, Robin Whitty, Vi Hart, and all the tauists who’ve reached out about $\tau$ in the past four years. Here’s to another great year ahead for $\tau$!

Michael Hartl, Tau Day 2014

### State of the Tau 2013

It’s been a big year for $\tau$. When I launched The Tau Manifesto back on Tau Day 2010, I hoped that $\tau$ might strike a chord, but its popularity has exceeded my wildest expectations—due in large part to the efforts of the many ardent tauists who picked up $\tau$ and ran with it. Now three years on, activity surrounding both the constant and the notation continues apace. In honor of Tau Day 2013, I’ve listed below some of the highlights from the last year. Enjoy, and Happy Tau Day!

Michael Hartl
Founder, Tau Day
Author, The Tau Manifesto

Note: I’d like to thank Joseph Lindenberg, Robert Palais, Robin Whitty, and Peter Harremoës for their help in compiling this list.