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Today is ‘Pi Day’, because it is March 14. You know, 3/14. Here is the definition: **π** (written ‘pi’ the Latin name of the Greek letter π) is a mathematical constant whose value is the ratio of any Euclidean plane circle’s circumference to its diameter. Maybe you are wondering why pi has its own ‘day’. Wikipedia provides some interesting information: ‘* Larry Shaw created Pi Day in 1989. The holiday was celebrated at the San Francisco Exploratorium, where Shaw worked as a physicist, with staff and public marching around one of its circular spaces, then consuming fruit pies. The Exploratorium continues to hold Pi Day celebrations*‘.

Now you know how it started. Pi Day is celebrated by math enthusiasts and geeks around the world on March 14th. But everything is not perfect in the ‘world of pi’… This morning I read an article on CNN by **Elizabeth Landau**: ‘On Pi Day, is ‘pi’ under attack?‘. You read well, some people don’t see things they way the rest of the world does:

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*But amid all this celebration, there lurks a force attempting to disrupt the revelry and push self-proclaimed pi nerds in a new direction. It’s called tau. Tau, technically, is just pi multiplied by 2, so about 6.28. But Michael Hartl, a physicist by training who’s now an educational entrepreneur, considers this number a more elegant and appropriate circle constant than pi and thinks pi should be replaced by tau across the field of mathematics (with the proper factors of 2, of course). He’s not denying the historical importance of pi, but he thinks it’s time to set the record straight*

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Feeling lost? Then read The Tau Manifesto on **Michael Hartl**‘s website and… You will feel even more lost than you already were! Seriously. This manifesto is worth reading and the approach is interesting even if you are not a mathematician, you will understand what it is about.

If you are into goodies, you can buy Pi T-shirts here and of course, Tau Day T-shirt on this page. I already have a very used Pi T-shirt maybe it is the occasion to switch for a Tau Day T-shirt… Now let’s eat some pi~~e~~! ^_^