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On Fri, 4 Apr 2014, Mark Evans wrote:
On 04/04/14 11:26, Eion MacDonald wrote:On 03/04/2014 23:06, Julian Hall wrote:With a SatNav it doesn't matter if you can't see anything as long as you can see /it/.AND you do not move except very cautiously. SatNavs for civilian use are not accurate within 6 feet (deliberately). So easy to walk over an edge. USA military accuracy is 10cm!IIRC this inaccuracy can be turned on and off. (Though for a large chunk of the planet at a time.)
It was turned off in 2000 and the US govt. have promised to keep it off. The "selective" part of SA was name as they could select which continents it applied to - the sattlites turning the wobble factor on or off as they passed over...
But with the advent of dGPS it doesn't make any difference if it's on or off. It was pointless, really, and why they didn't think of that in the first place is anyones guess.
It may even be off at present due to a combination of US soldiers being issued with "civilian" units (easier to get hold of in quantity at short notice) together with the possibility of competition from the EU and the Russian Federation.
Gulf war - 1991 and they had to turn off SA to make the civilian units be of any use to them at that time, but it was turned on again and remained on until Carter signed an agreement in 2000 to keep it off.
Gordon -- The Mailing List for the Devon & Cornwall LUG http://mailman.dclug.org.uk/listinfo/list FAQ: http://www.dcglug.org.uk/listfaq