title: How to interpret the accelerometer readings from iPhone
body: <p>I am trying to build a Kinect and iPhone based application.</p>
  
  <p>I am trying to compute the acceleration of my hands over time on each of the X Y and Z axis based on the trajectory returned by the kinect. Basically I am selecting a standard time interval of 0.5 seconds or 15 frames( <code>dt</code> ) and 3 points, ( <code>x0</code>, <code>x1</code> and <code>x2</code> ) over time which are separeted by 0.5 seconds. First I should mention that the position of the 3 points is mentioned in meters. By using these points I am computing two speeds(<code>v0 = (x1 - x0) / dt</code> and <code>v1 = (x2 - x1) / dt</code>). Finally, by using these speeds, I am computing the acceleration between <code>x1</code> and <code>x2</code> as <code>acc = (v1 - v0) / dt</code>.</p>
  
  <p>I repeat these computation at each frame and I obtain an array of accelerations.</p>
  
  <p>As I've said, I have also an iPhone and I want to see in which hand I have my iPhone, left hand or right hand. I want to do this by trying to match the accelerations of my hand with the accelerations of the iPhone held in the right position so that I have the same axis system.</p>
  
  <p>The only problem is that there is a huge difference between my accelerations and the accelerations of the phone.</p>
  
  <p>The phone acceelaration readings are somewhere between -2 and 2 for each axis, whereas mine are between -10 and 10. How should I interpret the iPhone accelerations in order to obtain similar measures to mine in meter / seconds ?</p>