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Supatramp
Occasional Visitor
Joined: Nov 21, 2003
Posts: 38
Location: Scotland
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 Posted: Tue Jul 26, 2005 5:35 pm Post subject: GPS/speed accuracy |
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I've recently bought a Classic Road Angel.
The accompanying instruction booklet states that the speed readout given by the RA is extremely accurate. Does this just apply to the RA or is it to do with the connection to GPS??
With one of our cars, the speedometer is over-reading by 5mph, and a friend has made an interesting comment; if the speed given by the RA is indeed accurate, then not only is the speedometer over-reading, but the mileometer is showing a higher mileage than the car has actually done!!
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caravanj
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Joined: Nov 01, 2004
Posts: 72
Location: Gainsborough UK
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| Posted: Tue Jul 26, 2005 7:08 pm Post subject: |
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| The speed accuracy for my Inforad unit is 0.62MPH. Car speedos can be as much as 10% out. |
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DennyL
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Joined: Jan 24, 2004
Posts: 114
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| Posted: Thu Jul 28, 2005 10:33 am Post subject: |
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| Quote: | | a friend has made an interesting comment; if the speed given by the RA is indeed accurate, then not only is the speedometer over-reading, but the mileometer is showing a higher mileage than the car has actually done!! |
I don't think the car's system for measuring the distance it has travelled is related at all to its speedometer. It would be unecessarily complicated to derive distance from speed. |
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neil01
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Joined: May 06, 2005
Posts: 902
Location: Leeds
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| Posted: Thu Jul 28, 2005 1:39 pm Post subject: |
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| DennyL wrote: | | I don't think the car's system for measuring the distance it has travelled is related at all to its speedometer. It would be unecessarily complicated to derive distance from speed. |
Quite the opposite - it would be more difficult and expensive to have two sensors, one to recore speed, and another to record distance. Ater all speed is only distance related to time. You only have to look at a speedo to see that it often only connects to one sensor to see that the two can be linked.
Back to the original point; what you have to take into account is the way in which GPS calculates speed - it is NOT your CURRENT speed, it is a historical figure and a few seconds out of date. The ONLY time it can be compared against you speedo is when you are travelling at a constant speed (and possibly in a straight line on the level - since (not 100% sure) but I think that it displays velocity rather than speed). Also the accuracy may be dependant upon the number of satallite fixes. |
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