Three months ago the world (or at least the geek world) celebrated Pi Day of the Century (3/14/15...). Today (6/28) is another math day: 2π-day, or Tau Day (2π = 6.28319...). Some say that Tau Day is really the day to celebrate, and that τ(=2π) should be the most prominent constant, not π. It all started in 2001 with the famous opening line of a watershed essay by Bob Palais, a mathematician at the University of Utah: "I know it will be called blasphemy by some, but I believe that π is wrong." Which has given rise in some circles to the celebration of Tau Day—or, as many people say, the one day on which you are allowed to eat two pies. But is it true that τ is the better constant? In today's world, it's quite easy to test, and the Wolfram Language makes this task much simpler. (Indeed, Michael Trott's recent blog post on dates in pi—itself inspired by Stephen Wolfram's Pi Day of the Century post—made much use of the Wolfram Language.) I started by looking at 320,000 preprints from arXiv.org to see in practice how many formulas involve 2π rather than π alone, or other multiples of π. Here is a WordCloud of some formulas containing 2π: