On Fri, 04 Jul 2008 15:53:58 GMT, "Graham" wrote:

Thanks for the rapid information Vic and to all the others who have posted
interesting comments here

The gps input helps measure the actual speed made good over the ground which
is needed for calculation of best speed for fuel consumption in litres/km
relative to the ground which is what I'm interested in (ie starting and
ending points of my trips are attached to the earth!)

I give up. :)