In what unit is the value given by magnetometer?

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CMDeviceMotion which gives the calibrated values gave me normal readings in μT, microtesla. (x: -7, y: 7, z: -44).

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it should be tesla (in SI)


Magnetic fields[edit]

Magnetic fields are vector quantities characterized by both strength and direction. The strength of a magnetic field is measured in units of tesla in the SI units, and in gauss in the cgs system of units. 10,000 gauss are equal to one tesla.[1]

Source: wikipedia


To check if it is nanoTesla or a different sub unit, measur the field in open space (far from any artificial magnetic field)


Knowing that the Earth's magnetic field can vary from 20,000 to 80,000 nT depending on location,


if you get a value in the tens of thousands (10 000 to 90 000), unit is nano Tesla.

If you get a value in the tens (10 to 90), then it is micro tesla

If you get a value in the ten millis (0.01 to 0.09), then it is milli tesla


What value do you get ?

I get 90 when reading x-axis. When calculating total magnetic influence I get 570. I used this formula to get the total magnetic influence: https://stackoverflow.com/questions/9349376/sensormanager-magnetic-field-range.



Using the raw data seem to be unreliable. Non understable?

https://stackoverflow.com/questions/47383128/getting-strange-magnetometerdata-in-iphone-when-programming-ios-app-with-swift


So I will probably go with the cmdevicemotion instead

https://developer.apple.com/documentation/coremotion/cmdevicemotion?language=objc.

Hardware specs are here, I believe: h ttps://www.akm.com/akm/en/file/datasheet/AK8963C.pdf


And I agree, raw data, in your app example/dev-level, is not meaningful. If the related API(s) won't cater to your (unstated) goals, feel free to file an enhancement request via the bug reporter link below, adding your report # to your thread for reference, thanks and good luck.

After searching, I think it is given in micro tesla (typical value is 45).


Have a look here

h ttps://www.kjmagnetics.com/blog.asp?p=iphone-fun

Surprised you get 570.


What are the 3 components of the field vector ?

It is (x: 92, y: 105, z: -551).

Which is the rawdata given by cmmotionmanager.


I downloaded a teslameter app which says (x: -14, y: 9, z: -40) μT in the same spot.

551 value is surprising.

May be you have some magnet that is perturbating the measure and creates a large vertical component.. It is very sensitive.


Try to measure outside, on open field, far from metallic parts…

CMDeviceMotion which gives the calibrated values gave me normal readings in μT, microtesla. (x: -7, y: 7, z: -44).

So, the answer to your initial post is : unit is micro tesla.


And you found out that CMDeviceMotion gives more credible values.

The total field is 45.1, which looks like Earth magnetic field.


Good luck for continuation of your project and don't forget to mark the thread as closed.