Just got Ultra Gauge today!

[Fat Charlie]

Euromodder- the gas stop was simply on the way to work, and as an added bonus it's at a light where I have to turn left. When traffic's light I can game the green light by waiting until someone else pulls up to it and trips the sensor. Then I start up and drive off through the now green light.

SentraSE-R- I will check the car against GPS, but I'll also have to see if I can figure out how accurate the GPS is being at any given time. The old PLGRs that I used to use would only give information as accurate as they could get, from a 4 digit grid (accurate to within 1km) up to a 10 digit grid (1 m). Today's smartphones whip everything up into a very pretty display, but the user is impossibly far removed from the actual data. How much of that log is hard data and how much of it is my phone making calculations based on spotty satellite readings and Google's map database?

I do trust the car, though. It was very well manufactured and its instruments have been... independently verified by various police departments over the years (a somewhat expensive and time consuming process, and always when I had somewhere that I needed to be in a hurry). Mile markers? I just can't bring myself to use street signs as precision measuring instruments.

[California98Civic]

Originally Posted by Fat Charlie

the gas stop was simply on the way to work, and as an added bonus it's at a light where I have to turn left. When traffic's light I can game the green light by waiting until someone else pulls up to it and trips the sensor. Then I start up and drive off through the now green light.

Nice tactical thinking, Fat Charlie! Darrell makes excellent points about the GPS and tire size and such, but your questions about GPS reliability make me wonder: which are the good GPS systems and how can a person tell before buying one? (I don't have one.)

[SentraSE-R]

Current GPSes are accurate to within 15 meters (~50 feet). That's not much error over a 10 mile distance. The different map databases and programming algorithms used by the GPS companies probably introduce more error. I know my Tom Tom GPS isn't nearly as user friendly displaying trip distance as my Garmin GPS or the Magellan I gave to my niece.

I've found mile markers to be notoriously inaccurate. The highway workers and contractors will straighten a road, and move milepost 3 to the 2.8 mile location. Highway departments used to have speedometer test sections. I haven't seen one in decades.

[Fat Charlie]

My issue with GPS isn't how much accuracy the system is capable of when locating a particular point, my issues are with how much varying accuracy and refresh rates are combined with map databases, churned around in a computer program and spat out as route information.

I've watched the number of satellites that my system was tracking fluctuate and the quality of grid it was able to give me fluctuate along with it. You can lay a slick UI on top of that to give pretty pictures and reports, but that UI is making a lot of assumptions. I'm going to use Torque and My Tracks to see how close they are, but I lean towards trusting a rev counter and OE tire size. At least I know for a fact that they account for elevation changes.

[Xist]

Originally Posted by Fat Charlie

If I'm calculating the mileage with my odometer, I'm going to calibrate the UG to the odometer.

I understand your perspective, but the manual states: "NOTE: Using the vehicle's odometer to perform this calibration is pointless since the odometer and UltraGauge receive distance information from the same source."

--Xist, the necromancer!

[California98Civic]

Originally Posted by Xist

I understand your perspective, but the manual states: "NOTE: Using the vehicle's odometer to perform this calibration is pointless since the odometer and UltraGauge receive distance information from the same source."

--Xist, the necromancer!

FWIW, my UG often shows slightly different numbers than my ODO. Off by one or two miles.

[Xist]

Originally Posted by California98Civic

FWIW, my UG often shows slightly different numbers than my ODO. Off by one or two miles.

Everyone seems to feel that a GPS is the ultimate in geographical accuracy and maybe it is, but my mother has mine and while she keeps telling me that she will return it, I worry that I will need to drive up there to get it.

I do not know how accurate mile markers ever were, but a margin of error of less than a mile should be adequate for most purposes. As for my odometer, I would expect that to vary fractionally as my tires wear out. Yes, mile markers may be put in the wrong spot after construction, but what if they made the highway longer or shorter, wouldn't that make the rest of them inaccurate, too?

From one mile marker to the tenth subsequent, my odometer showed 10.163 miles. For all that I know, both are inaccurate.

[Smurf]

As far as I remember, we were required to put mile markers exactly every 1.00 mile, unless there was an on-ramp or other obstruction, when I worked on the highway crew. Also, the delineators (spell check?) should be exactly 1/10th of a mile, except around curves and on-ramps, where it goes to 1/20th of a mile.

I'm not saying the bossman would grab his surveying equipment to verify each post, but I'd generally trust those markers more than my odometer.

(edit; We didn't measure the distances personally, it was all from the blueprints)

[campisi]

Originally Posted by SentraSE-R

Current GPSes are accurate to within 15 meters (~50 feet). That's not much error over a 10 mile distance. The different map databases and programming algorithms used by the GPS companies probably introduce more error. I know my Tom Tom GPS isn't nearly as user friendly displaying trip distance as my Garmin GPS or the Magellan I gave to my niece.

I've found mile markers to be notoriously inaccurate. The highway workers and contractors will straighten a road, and move milepost 3 to the 2.8 mile location. Highway departments used to have speedometer test sections. I haven't seen one in decades.

That accuracy is PER POINT! Not over 10miles.

[GRU]

My magelan GPS is not accurate for speed. I have done coastdown testing and once in neutral coasting (slowing down) the gps would sometimes go up in speed which would be improssible, not by much but still, i don't think it should be showing higher speed when there is no way i was accelerating...and sometimes when i'm crusing at a steady speed it would show me anywhere from 2 to 3 km/h difference when my speedometer/torque app is showing a steady speed.