PC Demo UI Lite v4.1.3 - MPU6050 software that is compatible with the evaluation board of the MPU6000 seems to have a fixed real world axis system assuming it uses the compass on the other hand when we only use MPU 6000(without the compass) the quaternion out-put seems to change the real world axis system according to the power up orientation. In simple words the axis system vary when we only use the 6-axis MPU6000. But int the PC Demo UI Lite v4.1.3 - MPU6050 software with the help of compass make a fixed axis system. It seems to like this software only demands the raw data inputs of gyroscope, accelerometer and magnetometer then they are converted to calibrated data and some how that data is then converted to quaternions relative to a fixed axis system for my application varying the x,y axis with power up position make a great error so how these calibrated sensor data are calculated and then how to convert them in to quaternions after figuring out a real world fixed axis system?