In message , at 18:37:46 on
Tue, 31 Aug 2004, Derek * remarked:
I have a Toyota previa with built in satnav. It is supposed to have
inputs from speed sensors and steering sensors.

What those do is allow the system to continue working in mostly urban
environments with lots of buildings, where the view of the sky is
obscured.

One day my boss came over from Holland with his PDA running tomtom. We
had them both running together with the same destination set on a trip
over the pennines on the small roads.

Which doesn't describe roads in the Pennines.

Without fail they came up with identical
directions at the same time the PDA usually less than a second later.

One could have been forgiven for thinking they were using the same
basic "engine" and the same basic map (which might I suppose be the
OS!).

Very likely. I had a Honda with Satnav and it undoubtedly used the same
mapping as Microsoft MapPoint - it had the same silly mistakes in the
data!
--
Roland Perry