```Issue #4897 has been updated by drbrain (Eric Hodel).

=begin
Martin, you are right.  With a corrected benchmark there is an 8.5% +/- 1.2%:

x tau.txt
+ 2pi.txt
+--------------------------------------------------------------------------+
|xx      x x                              + +      +     +                 |
|xx x    xxxx x x           x    +  + + + + +++ +  + +  ++   + +          +|
| |______A_____|                       |________MA_________|               |
+--------------------------------------------------------------------------+
N           Min           Max        Median           Avg        Stddev
x  20      0.526745      0.557717      0.535967     0.5353094  0.0073255609
+  20      0.562776       0.60921      0.579785     0.5810366   0.011508619
Difference at 95.0% confidence
0.0457272 +/- 0.00617423
8.5422% +/- 1.15339%
(Student's t, pooled s = 0.00964656)

=end

----------------------------------------
Feature #4897: Define Math::TAU and BigMath.TAU. The "true" circle constant, Tau=2*Pi. See http://tauday.com/
https://bugs.ruby-lang.org/issues/4897#change-37198

Author: sbaird (Simon Baird)
Status: Assigned
Priority: Low
Assignee: matz (Yukihiro Matsumoto)
Category: core
Target version: Next Major

Firstly please read the Tau Manifesto at http://tauday.com/ . It's quite long but essential to understanding why this is a good idea.

Here is a patch on trunk that implements this:
http://simonbaird.blogspot.com/2011/06/tau-in-ruby.html

Allow me to anticipate and respond in advance to some common objections:

1. It's easy to define it yourself so why put this in core.
Possibly correct, but I think this is the right thing to do. Tau is important. And it's a pretty small patch.

2. If this constant goes in then pretty soon someone will want every other math constant and there are hundreds of them. (Slippery slope argument).
The circle constant is one of the two most important numbers is mathematics. It's not just another math constant. We already define Pi.

--
http://bugs.ruby-lang.org/

```