Author Topic: Calibrate distance with a GPS? Better than mile marker method?  (Read 3935 times)

Offline beveryafraid

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I did the distance calibration, which to say the least was a bit harry since the traffic in my area is always fair to heavy. Kinda inconvenient to have to pull off of the road twice also, since you have to pull back into to traffic from the side of the road. I am also having serious doubts about the accuracy of this method. I set one of my car trip meters  ( I have two in my Honda ) to zero and the one on the UG to zero at the same time. After 75 miles my car meter read 75.5 miles and my UG read 75.3. This means that after 750 miles of driving there would be a disagreement of 3 miles between the two and at 7500 miles there would be 30 miles difference!!!

Which is more accurate? How do you know that the mile markers in your given area are laid down to a accurate spec?? In the past I always noticed a discord in the trip miles between my GPS and my car trip meter too. I always figured that since I get 3D differential accuracy on my GPS ( good reception of satellites and an accuaracy within 15 feet ) that the GPS would be the more correct instrument in this case.

What do the UG company engineers, or at least the admin guy in here think about using GPS,  ( like say after about a 20 to 100 mile drive ) to use to set the distance calibration instead of unreliable mile markers?

Offline beveryafraid

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Re: Calibrate distance with a GPS? Better than mile marker method?
« Reply #1 on: May 15, 2011, 09:07:50 PM »
Ok, I just went on another car trip, mostly on the interstate. This time I took my GPS along, which I had stupidly forgot to do on the previous trip. I left my driveway after zeroing the trip meter on my GPS, my car and the UG. When I got back I had the following three varying mileage readings:

GPS ------------- 71.6 miles
Car tripmeter - 71.2 miles
UG tripmeter -- 70.8 miles

This means that my distance calibration was probably better out of the box then it was after I did a two mile marker calibration recommended in the user manual!!!!! The calibration factor after going between two markers and setting my calibration to 2.00 was .981 and now after I reset it the calibration to match the 71.6 miles recorded on my GPS, the factor is now .992. If one then assumes that the factory sets this at 1.000, then my unit was probably a bit closer to reality before I did the mile marker calibration method. And therefore I would have been better off not doing the mile marker thing, which was almost dangerous in the heavy traffic I was facing at the time.

After the GPS trip, if my UG mileage would have been somewhere in between the mileage recorded by the GPS and the car's built in trip meter, then I probably would have left it alone. But since the UG reading was by far the lowest and I feel the GPS is more accurate of the all of them, I went with it's reading instead. So I don't necessarily recommend the method of using mile markers that the manufacturer recommends. If you have a GPS or know someone that does and will let you borrow it, use it instead. Apparently some municipalities do not use an accurate method of setting the distance between markers and you can't count on it.
« Last Edit: May 15, 2011, 09:16:11 PM by beveryafraid »