updated 03:36 pm EDT, Wed October 16, 2013
Supplier switch leaves phone with offset bias
The problems with motion sensing in the iPhone 5s are indeed connected to hardware, suggests RealityCap CEO Eagle Jones. Jones notes that whereas previous iPhones were based on STMicroelectronics accelerometers, the 5s uses a Bosch Sensortech part. Both sensors have similar variance, but the Bosch part has higher bias, noted to be consistent with the inaccuracies people are seeing in iPhone apps. Jones estimates an offset of +/-5 degrees, versus just +/-1 degree for the STM accelerometer.
He argues that Apple could have fixed the problem with factory calibration, but simply didn't, for whatever reason. As a stopgap solution, it's recommended that app developers include calibration procedures allowing users to set their own zero points.
RealityCap is working on code for developers meant to fix the problem without having to write unique solutions each time. That technology is still under development, though, and won't be formally revealed for several weeks. Apple itself could conceivably update iOS 7 to make software calibration universal.