Why HMDDevice->GetCurrentOrientationAndPosition() return a different position?

Can anyone explain to me why HMDDevice->GetCurrentOrientationAndPosition(rot, pos) return different pos while I only turn around my Oculus in a fix position? Isn’t the return pos is the location offset from the associate Pawn? Also is the rot and pos information return from GetPositionalTrackingCameraProperties() and GetCurrentOrientationAndPosition() are the same all the time?