In message
, at
05:02:55 on Tue, 12 Feb 2008, Mizter T remarked:
I've never really used a sat-nav system

Do they display a GPS speed? I use a rather older handheld GPS system
(that doesn't have maps).

to compare true speeds with indicated speeds, so I've never really been
aware of the difference between the 'true' speed I've been travelling
at as opposed to the 'indicated' speed.

My current car indicates 60mph at a true 56mph. And similarly pro-rata
at higher speeds.

I guess that implementing a very accurate vehicle speedometer system
is hard to do, so I wonder if most vehicle (and in particular car)
manufacturers design their speedometers "on the safe side", so as to
indicate a faster speed than the true speed - based on the rationale
that it's better for drivers to think they're going faster than they
are, rather than think they are going slower than they are?

They are legally required to. Any error *has* to mean the speedo is
over-reading.
--
Roland Perry