How to get iOS accelerometer axis right when changing device orientation?

I'm making an Unity iPad application with support for Landscape Right and Landscape Left and Auto Rotation. How can I detect Landscape Left or Landscape right, to use the accelerometer input right? DeviceOrientation has too many options, I need to detect if the current iPad system rotation is Landscape Right or Landscape Right, not interupted by all the other values of the DeviceOrientation class.