I have several models of GPS unit and verified my L spedo. At 70 miles the reading was of 1.5 miles reading 68.5 on all unit +/- a .1 on all units. The Military has turn off (SA) that give error to cilivan GPS unit so the offset should be correct using the GPS to verify the trucks spedo.

Dave

 

I beg to differ on your post about the error being corrected at present. The G has recently given the OK but it hasn't been implemented as of yet..With the lag on update this would still be difficult to use as a reliable method of speedo calibration, but I guess it is the next best thing to a certified speedometer. I have the good fortune of having the info pertaining to GPS through the system that the Chicago Fire Department is currently using, and even we can't have the error free operation as of yet. We still operate with about a 40- 50 yard error factor. This would account for some if not all of your differentiation. Hope this helps you some.

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FIRESVT Red 2000 "L"
Just starting
Still in a learning curve mode.

 

FIRESVT- You need to go to www.garmin.com, then under "What's New", Announcements, -SA Discontinued. They have set SA to zero (0)as of 1 May, 2000. They have all the information and the White House press release.

Dave

 

Even with SA turned off, there is still a 10 meter error. How this affects speed is determined by the PDOP at that particular point in time. It is still more accurate than most factory speedo's. I checked mine using a really good GPS with PPS, and found 1-2 MPH difference at 60mph.

 

What a surprise, as a director of a company (CyberLocator) that uses GPS technology to authenticate end-points on a network, I was delighted to see so many up to date members. I used GPS during One Lap last year (Garmin Street Pilot) and I can tell you that it was always within 1 mph of the indicated speed on the speedometer. The Street Pilot allows you to set an audible speed alert (we used 90 until too many complaints from co-drivers trying to catch some sleep).

 

I worked for Magnavox Advanced Products for over 18 years ( Before they sold us). If my memory serves me right, we were the ones that came up with SA for GPS for the Government. I remember the Old navigation systems Omega (lanes 8 miles wide) and then transit ( might be 90 minutes till next your satellite fix). And now soon cell phones with GPS for 911 calls!

Dave