Glicko 2 Formula

I'm trying to learn about glicko 2 rating system . In that document, there is a formula in step 5, point 2 that says $$B = a - k\sqrt{\tau^2}$$ Can anyone explain what is the point of squaring the tau, then getting its root again?

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$$\sqrt{\tau^2}=|\tau|$$ ${ } $${ }$$ { }$

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Alright, thanks. I was worried that I missed something out, because the value of tau is supposed to be between 0.3 and 1.2, and they have used || to indicate absolute elsewhere. –  ananda Oct 5 '12 at 7:45