Hello,
Yes, in the absence of linear acceleration, the accelerometer output is a measurement of the rotated gravitational field vector and can be used to determine the accelerometer pitch and roll orientation angles. Take a closer look at the AN3461 providing both the theory and mathematics of orientation determination using a three-axis accelerometer.
Accuracy basically depends on the level of calibration on a final product. This involves placing the final product at multiple orientations and calculating 12 additional new calibration parameters which must then be stored in non volatile memory and applied by an external MCU. There is the AN4399 explaining how to do this. We recommend the 12 point algorithm that corrects for a 3x3 gain matrix and 3x1 offset vector. Our measurements on MMA845x family, MMA8652FC and FXOS8700CQ accelerometers indicate that after application of this algorithm, the resulting error is 3mg RMS in each axis. That corresponds to an RMS angle error of 0.17 deg RMS.
Hope it helps.
Regards,
Tomas
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