How to calculate rotation around its own axis, knowing the angles of declination along the global axes?

Question

Mathematics

There is a phone that returns the angles of deviation from the global axes. How can one calculate the angle of rotation around the screen normal from them? Or where to dig?

Answer 1

As a rule, the API returns exactly this angle and 2/3 more others as angles of deviation from the global axes. Therefore, you just need to choose the desired angle from the received ones.