The order in which the matrices are applied is important, because the matrix multiplication is "not" commutative. This also applies to the three rotations, as can be demonstrated by an example: The point (1, 0, 0) lies on the X-axis, if one rotates it first by 90° around the X- and then around The Y axis, it ends up on the Z axis (the rotation around the X axis has no effect on a point that is on the axis). If, on the other hand, one rotates around the Y axis first and then around the X axis, the resulting point is located on the Y axis. The sequence itself is arbitrary as long as it is always the same. The sequence with x, then y, then z (roll, pitch, heading) is often the most intuitive, because the rotation causes the compass direction to coincide with the direction of the "nose".