Is the iPhone accelerometer calibrated? Gravity measurement changes depending on orientation

Question

I'm doing some test with iPhone 4S accelerometer. If I take the raw data in Z-axis (telephone rest over desktop) I get an acceleration 9.65-9.70 m/s2 (after g conversion by 9.8261). But if i have the telephone resting over edge, the measurement of the accelerometer value in the X-axis is so different, aprox. 9.80-9.85 m/s2 (after the same g conversion). My question is, if the gravity is the same, why this difference? It is not callibrated?

On the other hand, I check the module value at both situations and the difference is the same. Thanks.

Answer 1

I don't know what kind of answer you expect, but you should be more precise when you're talking about calibration.

Of course, the g-sensors are calibrated and as always: every calibration comes with an error. In your case the error is under 1%.

So if you want an answer:

Yes, the iPhone accelerometer is calibrated and has an error under 1% in your case. If you collect measurements from other (hundreds of) users, you could calculate the mean error of the device (I guess it's about 1% though).