Thats 30 degrees from the imaginary centre line between the listener and the line that would run from speaker to speaker making a right angle with the centre line.
Code:
-----------------------------
 L                          R
  \            |           /
    \          |         /
      \        |       /
        \   30 | 30   /
          \    |    /
            \  |  /
             :lol: