title: Calculate degrees for movieclip rotation
body: <p>I've a movieclip representing an arrow (with registration point in its middle). When I click a button, the arrow must point to a certain movieclip on stage. I use this code to execute the Tween:</p>
  
  <pre><code>TweenLite.to(arrow_clip,1,{rotation:degrees});
  </code></pre>
  
  <p>but I can't understand how to calculate the degrees. 
  I tried the following with no luck:</p>
  
  <pre><code>var degrees =Math.atan2((clip.y-arrow_clip.y),(clip.x-arrow_clip.x))*(180/Math.PI);
  </code></pre>
  
  <p>Can you help me?</p>
  
  <p>[EDIT]: I found the following is working but I can't completely understand why:</p>
  
  <pre><code>var degrees = -(Math.atan2(arrow_clip.x-clip.x, arrow_clip.y-clip.y))*(180/Math.PI);
  </code></pre>