Speedo accuracy got me thinking....

[Bcc212]

Absolutely.

[lol-lol]

If you look in the literature with any consumer GPS device the accuracy is listed as within 5%.the accuracy can vary by up to this much in either direction. I certainly wouldn't risk my license on it.

 

When we first used GPS at sea on Naval vesels, around 1979, it would have us going backwards when we were actually going 18 knots forwards, not a great product for £12K at the time.

 

When the SA military component was deactivated, to make it less easy to hit hardened missile silos, we all got the accurate readings.

 

Main thing with SATNAVs are that they are preety slow to refresh ie 1,2,3 seconds so is pretty useless if you are blipping your speed rather than cruising.

 

 

"GPS for everyone

Initially GPS was only intended for military use. But then tragedy struck. On 1st September 1983, Korean Airlines flight KAL007 from Anchorage to Seoul strayed off course into USSR airspace and was shot down by a soviet Su-15 fighter jet. All 269 passengers and crew were killed. Two weeks later, US President Reagan proposed GPS be made available for civilian use to avoid navigational error ever again leading to such a catastrophe. While by no means the only reason, the Korean Airlines disaster was certainly a major catalyst toward civilian access to GPS.

Selective Availability (SA)

Having spent some $12 billion to develop the most accurate navigation system in the world, the US government then built a function called Selective Availability (SA) into NAVSTAR that would limit its accuracy for civilian users to ensure no enemy or terrorist group could use GPS to make accurate weapons. It worked by introducing deliberate errors into the data broadcast by each satellite. Military users could access the fully accurate system by decrypting a secured second frequency that was broadcast simultaneously. Then during the Gulf War the US military needed many more GPS receivers than it had. It solved the problem by using civilian GPS receivers. But to increase the accuracy of these devices, the SA function had to be temporarily disabled. Then in 2000, US President Clinton announced that SA would be disabled completely. Because US government ‘threat assessments’ concluded that removing SA would have minimal impact on national security. Though in the same speech he said the US would still be able to ‘selectively deny’ GPS signals on a regional basis when national security was threatened."

 

http://www.tomtom.com/howdoesitwork/page.php?ID=6&CID=2&Language=1

[Richf]

I used to be involved in a club that built and ran motorcycles that could achieve and exceed 200mph , we used to use a timing trap like they do in drag racing, the difference between the trap speeds and gps speeds could be quite significant

[WeirdKerr]

Maybe your work keeps moving

 

well they do.... they move folk, I work for a moving company, but they have been in the same place for 10 years

[lol-lol]

I gather we are moving at several million miles per hour from the point of the big bang !