title: Instruments doesn't show Energy Usage Level: it is empty
body: <p>I have followed the Apple steps to get my app energy usage level from my device using Energy Diagnostics Instruments (https://developer.apple.com/library/ios/#documentation/DeveloperTools/Conceptual/InstrumentsUserGuide/Built-InInstruments/Built-InInstruments.html#//apple_ref/doc/uid/TP40004652-CH6-SW63).</p>
  
  <p>I have tried with my own app and with several apps from the AppStore and I always get all the info expected (including time flags) except the Energy Usage Info. 
  Simply, the Energy Usage Bar doesn't show any graph (it does show the running time) and the Energy Consumption table (detail view) is always blank.</p>
  
  <p>I am using an iPodTouch4 and XCode 4.2. 
  What could be the problem? Do I need to do anything apart from Apple steps? </p>
  
  <p>Thanks in advance.</p>