I tried this but it dont work as I expected(the results in euler had to be the same)...

```
Quaternion relative_rot = Quaternion.Inverse(transform.rotation) * Quaternion.LookRotation(Vector3.up);
Vector3 relative_rot_euler = relative_rot.eulerAngles;
Debug.Log("x,y,z : x1,y1,z1 "
+transform.rotation.eulerAngles.x+", "
+transform.rotation.eulerAngles.y+", "
+transform.rotation.eulerAngles.z+" : "
+relative_rot_euler.x+", "
+relative_rot_euler.y+", "
+relative_rot_euler.z );
```

The primary idea is to measure deviation of direction in euler angles from one vector3 to another.