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\draw (0,0) -- (60:.75cm) arc (60:180:.75cm);

What does the colon in (60:.75cm) mean? Normally, I'd define a normal point there.

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  • Figured it out and wrote a neat answer, but apparently I can't post it within 8 h of asking, it told me AFTER letting me write the answer!! (this is a bug report) – Nazia Mar 7 '12 at 20:32
  • That's hilarious, the same second! – Werner Mar 7 '12 at 20:37
  • @Werner Well, that's a first. – Torbjørn T. Mar 7 '12 at 20:38
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The colon signifies that polar coordinates are being used. (60:.75cm) means the point that is at an angle of 60° and a distance of 0.75cm from the origin.

In the TikZ/PGF manual this is mentioned in section 13.2 Coordinate Systems, p 125:

The implicit form for canvas polar coordinates is the following: you specify the angle and the distance, separated by a colon as in (30:1cm).

This also holds for other coordinate systems like xyz polar. Alternatively, if you're not interested in this shorthand notation, TikZ also provides

\pgfpointpolar{<degree>}{<x-radius>/<y-radius>}

where <y-radius> is optional. See section 70 Specifying Coordinates (p 571) of the documentation.

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