Interesting Link:

Pi or 2Pi: That Is the Question

In February this year there appeared in Physics World an article entitled Constant Failure by Robert P Crease of Stony Brook University, in which he showed in how many formulae of physics and mathematics 2π turns up, rather than π. This article struck a chord with me, since even after many years I remember the feeling of "cognitive dissonance" when being taught that the formula was 2πR rather than πD.

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