Right. That's it. We're convinced. We are officially behind team ! Pronounced "tau", 6.28318... There is a movement that it should replace the use of that favourite mathematical constant, . We're not sure if it's likely that will go gently into that dark night, but Phil Moriaty certainly makes a good case for the use of in teaching in this episode of Numberphile, released in honour of today being Tau day (June 28 is 6.28 when written in the US date format).

And Vi Hart explains that not only is the logical choice, it will return beauty to trigonometry...

Phew. Now we know that Euler's identity is safe in 's hand, we definitely vote ! Happy Tau Day everyone!

## Tau and Pi

Very welcome! I teach elementary trig using Tau and Plus's endorsement will help convince my students that I'm talking sense.

I hope Plus now becomes 'Tau Manifesto compliant' meaning Pi is not referred to except for historical reasons.

Robin Whitty

www.theoremoftheday.org