Sensors value dont understand

Hi,

Is it possible to know where is the algorithm who was used for the value “yaw”, “pitch” and “roll”?
Is it possible to know why the yaw value change when i turn the matrix creator between 90° , 70° , 60 ° then, 60°, 70°, 90° then 90°, 110°, 128° and 128°, 110°, 90° ?
there is not explications about that in the website …?

Thanks a lot.