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Comment by ianterrell | Hacker News Reader

Pi is the wrong constant.

That animation looks great, but it's misleading: the fundamental measurement of the circle is the radius, not the diameter.

Measured with a unit radius, we'd see 2*pi for a full "turn" of the wheel. Twice pi, or tau, is the magic number.

See http://tauday.com/ for details.

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Random speculation: Maybe pi was chosen because the symbol for tau (τ) is hard to distinguish from a ‘T’ when hand-written?

BTW, I don't mean to take anything away from your comment; that link was awesome.

When π was "invented" it could have been 2 x 3.141. The author makes a case for tau because it is too late to redefine π

>Pi is the wrong constant.

Seems a bit pedantic. The post was about illustrating pi after all. I do enjoy the argument for tau though.

Actually I found that the animation showed a clear example demonstrating that pi is wrong. I don't know about you, but when I looked at it I immediately recognized the blue arrow and the centre of the wheel. That's a radius. There's no easy way to determine that a diameter was in the picture. As it rolls over the circumference, it's the radius line we follow. Therefore, I agree that pi is truly the wrong constant to show here. And it is wrong in a greater sense than what is presented at tauday. It's actually downright confusing or even misleading to highlight a radius and a circumference, and then talk about pi.

??? What do you think those vertical blue bars were all about?

I've read the Tau Manifesto before, and I think it makes some really good points. I'm probably 60-75% in agreement with it. But this animation is fine.

The animation itself admits the error by backing the circle up the distance of the radius before beginning rolling.

Pi is the right unit because it represents the largest irreducible radian size. It is the fundamental unit of 2 dimensional angles.

Only if all your shapes are convex. Arbitrary angles can be up to 2π.

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