How to use magnetometer with Location Beacons estimator

I would like to know more about estimometer magnetometer, I do not see any documentation in my account that obtube, I already created an application but I can not understand how to program it in android to detect a metal or a large object, I hope you can help me or if there is an example and if the type of bullets I’m using or which one I should use is ok.

Thank you very much for your help.
Good day