title: gauge: rotate the needle
body: <p>i'm building a gauge widget with raphaeljs, starting with
  <a href="http://renatoalbano.github.com/raphael-gauge/" rel="nofollow noreferrer">http://renatoalbano.github.com/raphael-gauge/</a> example..</p>
  
  <p>I don't understand what the criteria is for select a particular "center" for the needle:
  in the first example the center of the needle is [140, 5] and the second is [67, 13]... how the author calculate it?</p>
  
  <p>..and can i place the needle like this 
  <img src="https://i.stack.imgur.com/XVLoK.png" alt="gauge">
  or it's necessary to place it in the middle of the circle/gauge?</p>