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 expectationsâ€”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.

- The Massachusetts Institute of Technology (MIT) continued their tradition (established last year) of releasing their admissions decisions on Pi Day at Tau Time (i.e., March 14 at 6:28pm)
- Peter Harremoës’s paper “Information Divergence is more $\chi^2$-distributed than the $\chi^2$-statistics”, which uses $\tau$ for the circle constant, was accepted for presentation at the International Symposium on Information Theory, and a second paper using $\tau$ was submitted to the Information Theory Workshop; two more papers using $\tau$ for the circle constant have also been accepted
- Robert Bradley discovered that Leonhard Euler used $\pi$ for $C/r$ in
*Opera Omnia*(1747), sparking a series of discoveries by Joseph Lindenberg and Robert Palais that Euler went back and forth on the use of $\pi$ over the years—using it for $C/r$, $\frac{1}{2} C/r$, $C/D$, and even $\frac{1}{4} C/r$ - The Khan Academy added support for using tau when submitting answers
- Robin Whitty and Robin Wilson hosted a seminar on $\tau$ and $\pi$ at the University of Oxford
- Ben Hummon taught a calculus course at UC San Diego using $\tau$
- The popular YouTube channel Numberphile released three videos on $\tau$
- Robin Whitty’s website theoremoftheday became “Tau Manifesto Compliant”
- Wouter Vink used $\tau$ in the thesis for his master’s degree in mathematics from Utrecht University in The Netherlands
- Mathematics teacher Doug Kuhlmann from Phillips Academy gave a presentation on the advantages of using tau in the classroom at the Anja S. Greer Conference on Secondary School Mathematics
- Having filled up the Pi Building to capacity, the city of Bethlehem, Pennsylvania, began development on a new Tau Building for its innovative post-incubator workspace program
- The Processing computer language for creating images, animation, and interactions added a predefined TAU constant equal to $6.28\ldots$
- The Cadence Watch Company released the Tau Circle Watch
- LucasVB made an animated gif illustrating the geometric meaning of $\tau$