tpctl inacurrate or failing?

Hi all

I'm running into problem with tpctl on my 720; the way they look I
shouldn't be the only one, but here goes:

- I ran tpctl from the console as root
- made sure /etc/tpctl.dat was created and filled in
- added tpctl=YES to rc.conf
- /etc/rc.d/tpctl start -> "calibrating touchscreen..."
- so I launch xdm to check calibration

And no matter what I do, there is a skew. On most of the screen, the
pointer is off to the right from the stylus. The distance increases
the further towards the right you go, and a few other inaccuracies.
Makes it difficult to use WMs that use a panel, like IceWM or Matchbox.
I did a reboot in case I had overlooked something in the
initialisation, but that's changed nothing.
Tried re-creating the tpctl.dat a fair number of times as well.

This is on NetBSD-3.0-release; but has anyone seen a similar problem?
Maybe pinpointing what to look at might help; I thought about manually
editing tpctl.dat but the syntax is unclear.

Cheers

Michael