title: iPhone - understanding iPhone rotation
body: <p>I am banging my head on the wall trying to understand this. See the next picture.</p>
  
  <p>Suppose I have an iPhone resting on a table. At this time the rotation readings thru core motion are 0,0,0 for yaw, roll and pitch (picture A).</p>
  
  <p>Then I roll it 90 degrees. Now it is sitting on the table with its left side, home button on the right. Now it reads 0,0,0 (picture B).</p>
  
  <p>Now I yaw it 180 degrees. It is now sitting with its right side on the table. Home button on the left. It now reads 180,0,0 (picture C).</p>
  
  <p>The problem comes if I roll it now. Suppose I roll it -45 degrees. I should be reading 180,-45,0 but instead I am reading 180,-45,180???? (picture D).</p>
  
  <p>Why is that? Why is it giving me a value for pitch if I never changed that? How can be pitch influenced by a rotation in other angles? thanks.</p>
  
  <p><img src="https://i.stack.imgur.com/UL0RY.png" alt="enter image description here"></p>