: Sorry, i'm not good enough into GPS terminology, but does this mean that the
: gps can benefit from full accuracy in the gps signal availiable? I.e. that
: the position is calculated as accurate as possible?

: Totto

Pretty much. The system works by comparing signals sent from a number of (typically 3 or 4, sometimes more) satellites. The most important part of the signal is an accurate clock pulse. By comparing the relative "offness" of the clock signal between satellites (because the radio wave and therefor the clock signal) ONLY travels at the speed of light, the GPS can calculate your (and it's) location.

Because this was initially for military purposes, they messed up the timing slightly. Military GPS units were designed to take the messed up timing into account, and they are able to compensate for it and display an accurate location. Civillian GPS's are unable to compensate for this, and therefore always displayed your location incorrectly. Close enough for most purposes, but not accurately. For example, you might be sitting dockside at sea level, but your GPS would insist that you were actually 100 feet above sea level...

This "feature" has now been deactivated, so civillian units now display positions as accurately as the military ones.

By the way, during the Gulf War, the jitter was removed, because there were not enough "military" GPS's to go around.