Today is 6/28, which means it's Tau Day!
Tau, which is equivalent to 2 * Pi, sees it's usage in writing equations in a shorter form. For instance, the angle of a circle can be stated as either 2 * Pi radians, or Tau radians. Another, more complex example of where Tau would be better is in the equation of the period of a spring:
Here, we could replace the 2 * Pi with Tau, and everything would be great.
Below are a few approximations of Tau, based on equations that approximate Pi.