This is fairly easily possible (well, causing a GPS to misreport) as it is - poor old 007 wouldn't need to go further than the local Maplins and spend abot 15 quid :-)
Oh, you'd notice...
My Garmin unit tells you how accurate the readings are, like most do.
Switching it off again would now result in crashes everywhere as the reliance on GPS has risen thousand fold since SA was switched off.
You're right that the speedo error will not have any relation to the odometer reading, but there's other factors than the spring strength... Here's an interesting article on speedo calibration...
Andrew
-- SIII 88" | Member of Club Land Rover Ireland | |
I agree with Austin that the US Military would reapply selective availability at any time that they thought appropriate. One development now is that they can apply it to a selected area (rather than the whole globe) meaning that if you are not in their "area of interest" your should be OK. I ahave been unable, however to find out how discriminating they can be on the size of the area (keeping in mind that there are 24 GPS satellites (IIRC) to cover the globe).
Peter '93 Disco 200Tdi
Aust>
You are using a very unreliable point of reference to check your GPS against...
The UK law regarding speedos, and I assume this is pretty much standard, gives a maximum allowable innacuracy at a number of speeds. As the speed increases the tolerance increases too which means that most car speedos are most accurate at lower speeds. The 10% thing over simplifies the requirement and is almost useless as a reference. Most speedos seem to be most accurate at lower speeds and then become more inaccurate (in percentage terms) as speed increases. Whilst at 30MPH they may only be 1 or 2 MPH out, at 70 they are often closer to 12MPH out. An indicated
85MPH is often around 70MPH true speed.The following are the actual requirements:
indicated speed - minimum true speed (MPH)
35 - 26 40 - 30 45 - 35 50 - 39 55 - 44 60 - 48 65 - 53 70 - 57Under no circumstances should the speedo read less than the actual speed.
As you can see there is actually a 13MPH tolerance at an indicated 70MPH as opposed to 7MPH that the 10% rule would allow... the actual formula for this tolerance is (true speed/10) + 6.25
That doesn't rule out a "problem" with your GPS of course ! My Garmin 12 was very accurate from 10MPH through to 100MPH when compared to a calibrated Terratrip unit. in fact it was accurate enough that we used it to calibrate the Terratrip once or twice when we couldn't find a convenient measured mile.
cheers
Dave W.
On or around Fri, 27 Jun 2003 09:25:20 +0100, "zebedee" enlightened us thusly:
which is all fine until someone decides that there's a threat to the continental US which can be averted by turning SA back on, when they'd do so anyway.
but in general, I suspect you're right. I believe the demise of SA came about from the fact that in GW1 the troops on the ground found the military GPS ineffective (forget exactly why) and promptly acquired a bunch of civvy units, which of course couldn't operate accurately with SA turned on. People at the time reported a sudden increase in accuracy.
On or around Fri, 27 Jun 2003 10:05:04 +0100, Mother < "@ {mother} @"@101fc.net> enlightened us thusly:
yebbut, evil masterminds nicking it from the CIA makes a better film plot.
Hi Dave, I left out some information in the previous posting as I didn't want to belabour the point. Now that you have raised it, I checked the speedo using our Freeways measuring time over calibrated distances (provided by our local transit authority).
The statements in my previous post were correct (spoken as a research scientist of many years). :-)
Peter '93 Disco 200Tdi
Dave White wrote:
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.