title: Determine the Device Orientation and its resulting Angle on one Dimension?
body: <p>I have the following setup: </p>
  
  <p><a href="https://i.stack.imgur.com/re1nL.png" rel="noreferrer"><img src="https://i.stack.imgur.com/re1nL.png" alt="enter image description here"></a></p>
  
  <p>An iPhone lies with the display to the ceiling on a table (alpha = 0 degrees). When the iPhone is moved upwards like shown in the image above the alpha angle increases. </p>
  
  <p>How do I compute the value of the alpha angle without taking care of any other axes which could change. I am only interested in this one axis. </p>
  
  <p><strong>How do I get the correct alpha angle the iPhone has when lifting up from the table? How do I get notified when the value of alpha changes?</strong></p>