The R-7 has 2 IMUs. One is used by Vuforia exclusively, the other is accessible via the standard Android Sensor APIs. The 2nd one is mounted in the temple to reduce EMI interference generated by the glasses electronics, and calibrated in the factory to normalize any mounting variation.
Attached is a simple "Bubble" App that allows you to assess how well your R-7 is calibrated is all 3 orientation axises. See this article on IMU-Orientation if you have questions about how the R-7's orientation is determined via the standard Android Sensor APIs.
Also, here's a link to a sample App that displays a 360 degree VR scene. You can use this to gauge how well calibrated your IMU is, and also if the IMU is drifting at all. You should see the scene remain mostly stationary when your head is stationary. Click on the icon in the lower left hand corner of the App UI to make the scene full screen. If you put the R-7 down on a table, you will see the scene drift slowly if the IMU dynamic calibration accuracy is not high. You can increase the IMU accuracy by holding the R-7 and moving it in a "figure 8" motion while it is turned on.