Jitter & gradual decline in y value

[nihohit]

Hey,
I'm using the code

def updateView():
pptPOS = tracker.getPosition()
viz.MainView.setPosition(pptPOS)

vizact.onupdate(viz.PRIORITY_DEFAULT, updateView)

and later on, in a different function

viewPOS = viz.MainView.getPosition()
head.lookat(viewPOS,5,viz.AVATAR_WORLD)
neck.lookat(viewPOS,5,viz.AVATAR_WORLD)

which is a simple code to make the avatar look at the main POV.

Alas, the code doesn't work. When the function needs to be called, the avatar's head jitters and gradually descends, until the helmet moves significantly, when it jumps back up and then returns to the jitter-and-descent routine.

Attached in the files is a graph of the result of getPosition over time - notice that the Y line is gradually descending and more jittery then the other lines - which makes me believe this isn't a problem with the code.

Any ideas?