# Happy Tau Day!

Over at tauday.com, Michael Hartl makes an impassioned argument for why pi, which is the universal circle constant that describes the ratio of a circle’s circumference to its diameter, was wrongly defined. Instead, Hartl says the universal constant should have been defined as the ratio of the circumference to the radius, and thus should be twice the value of pi. He calls this number tau (another Greek letter), and his Tau Manifesto lays out his argument.

On the tauday.com site, you can read the manifesto, watch a video of him making the arguments, and even listen to it being played as music, or see an amusing, short video about pi and tau. Honestly, the short video at the bottom of the site is my favorite.

Anyway, let’s still eat some pie to celebrate this day, but let’s have twice as much of it!

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### Paul Thomas

Paul Thomas is director of mathematics for K12. Previously, he taught mathematics and computer science at the Thomas Jefferson High School for Science and Technology in Fairfax County, Virginia. While at Jefferson, he was a contributing author for the mathematics textbook series Mathematics: Modeling Our World. Paul also has managed corporate training departments, and developed classroom, computer-based, and web-based training products that have been used by companies such as Oracle, IBM, Microsoft, and Novell. He holds a B.S. in Mathematics and an M.S. in Operations Research from George Mason University.