how often should getRotationMatrix update?

Question

I'm currently just bliting a rotation matrix onto the screen. The source of which is "RT" from;

SensorManager.getRotationMatrix(Rt, I, accels, mags);

Where accels and mags are from the sensors. The getRotationMatrix, and its display, are triggered once for every update of the acceleration sensor.

Question;

How often should getRotationMatrix update? That is, change the values its outputting? It seems to be far too slow to be any use.

I mean, once every 2-3 seconds it gives a new matrix out, even though its triggered hundreds of times inbetween (with different accels and mags fed to it)

Does anyone successfully use getRotationMatrix from here? What speeds does it update? I'm using a HTC Legend, Android 2.1.

I'm sure it can't be meant to be this speed...must be something I'm doing wrong, but I'm running out of options.

Cheers, Thomas