ADXRS646 calibration

Dear All.

I have an application in which I have to measure the angle between a couple of rotating planar surfaces around a common joint.

Just for giving you a picture, imagine you have to open a book and measure the angle between the two rigid covers.

Such a rotation could be around 90deg. The relative rotation of the 2 surfaces is completed in 1 or 2 seconds so maximum rotational rate is 90deg/second.

The idea is to couple a gyro with one of these 2 planar rotating surface. (I choose the ADXRS646 for measuring the rotating speed of a the planar surface)

The gyro gives the angular speed of the phenomenon: if we integrate it, in theory we obtain the angle between the two planar surfaces (let's say one of them is kept fixed).

For integrating such an angular speed, I need to now the gain of the sensor, or in other words the conversion factor between the output voltage and the angular speed measured.

This factor seems to me unknown in the sense that such a value is declared as nominal value but it differ from one sample to another.

for me, it's not possible to calibrate the system on the field because I can't impose, by some mean, a reference rotational speed.

I read on the datasheet that is possible to adopt a ratiometric configuration for the sensor.

Is such arrangement the solution for overcoming the problem of the calibration ?

Could some one give me some help about this topic ?

thank you very much!