The 0g bias level can have any values inside the limits given by the specifications. First of all, are there some ICs that give access to the internal reference so that it is much easier to align the bias of the IC to the bias of the peripherical electronic board (amplifier) without the need to put the two axes X and Y parallel to the horizontal surface of the earth and then adjust the 0 bias of the board on it (without considering the Z alignment error with the package...) ? Or, some ICs that give not the already differentiated outputs but all the separate differential interconnections of the sensors to let us appreciate the positely or negatively difference when the sensor is unbalanced ? Then, considering (knowing) what is the 0g level value at a precise time on one of the two axes, will it be the same value at the same time to the output of the other axe ? If not, how the mixing of the two outputs can give a precise tilt measurement to have a change in ouput the same for every change of degrees indepedently of the orientation of the IC ?