Innacurate position on new Mk3 computer

[Womble]

Hi Folks,

I recently got my hands on a Mk3 computer out of a scrapped 5 series.

I have installed it, and it all works in theory, but the further I move away from home, the more inaccurate it becomes (up to a maximum so far of around 300 feet out of position).

It is detecting plenty of satellites, the voltage on the gyro is correct, and is increasing and decreasing in the right directions, and the wheel sensor number increases with speed.

Can anyone suggest what the problem might be? I've driven around 50 miles since installing it, although that has been mostly in small bursts. Does it need a reasonably long drive to give it time to calibrate itself properly?

It doesn't get completely lost, as it does from time to time snap to the correct location (which I assume is why it never goes further than 300 feet off) but it really is useless for in town navigation at the moment.

Please help!