why there is a difference in the magnetic values taken by different smartphones?

Question

I need to record the magnetic data in the same surface by two smartphones.

I find different values of the magnitude of magnetic field knowing that I put my smartphones in the same place end the same height. The magnetometers are YAS532(sensitivity 0.2µT/LSB, Measurement Range ±1200 µT ) and AK09911(sensitivity 0.6µT/LSB, Measurement Range ±4900 µT ).

Why the results are different while magnetic field is known to be constant and stable? How can I correct the values using the parameters of the magnetometers?

Answer 1

I am pretty sure the answer is just in the fact that you are using different sensors. I have not done much in this area, but simply from the robotics classes I took in school I know that different sensors, even of the exact same specifications, will just return different data, and the same sensor may even sometimes return different data. This is normal because there will always be random error. What you really need to do is take a lot of measurements and figure out what a normal range of error is, and then write your code based on that.

Answer 2

Electrical engineering says magnetic field cannot be same w.r.t place and time. Magnetic fields changes - like when you bring watch near to compass and also as when earth rotates it gets changed.

So even if with some (can't say what ?) method you've attained fixed magnetic field smartphone circuit shall be changing field readings for sure.