Gyroscope problem

Hi everyone.

I am making a simple testing app that display the acceleration along the device's X, Y and Z axis. I read the value from Gyroscope.userAcceleration (so gravity has been compensated for). When I run the app on my iPad 2, I get a small gravitational acceleration bias (this is not noise since it always point downward). But when I run this app on the iPad 3, the bias does not appear. Is the difference between different iOS device normal? or does it mean that my iPad 2 gyroscope is broken. Is it rare for the gyroscope to be broken (my iPad 2 is really new, I just bought it 2 weeks ago). Many thanks