Determine earth coordinates relative to IMU

[marcobarnobi]

Hi,
I am having some troubles using the code.
It works perfectly with the dataset provided, but when I use the samples obtained from my own IMU the output does not make sense . I think that this is due to the initial condition 'Quaternion=1 0 0 0', that represents the Earth relative to the sensor. Probably I should set my own 'Quaternion' as an argument of the MahonyAHRS function.
If this is right, how do I find this quaternion?

Please let me know. :)