How does the ScanGauge actually "calibrate" itself?

[metallickirby]

Ok. Need the help of all you ScanGauge owners.

I have had the ScanGauge for one week.

I originally put the speed offset to 2%. It seemed perfect. When the speedometer was 60km/h, the speed of the SG read 60.

Anyways, then I checked the distance traveled after about 60 km on the driveway. (I had reset my car's trip counter to see how accurate the SG was) Anyways, I found it was a 4.4km distance. The SG had read that I had traveled 4.4km less than it read on the car.

At this point, I changed the speed offset to 1%. This caused the SG to show 59 when 60 is showing on the speedometer, but the distance traveled coutner is much more accurate. Only differing by 1km every 40km. However, it bothers me a little that the speeds on the two are differing by 1km/h.

I haven't filled up twice yet with the SG installed to I have yet to set the offset for the fuel. (I will this weekend) Does anyone know if changing the fuel offset will affect the distance traveled calculations? What if I changed the speed offset back to 2% and adjusted the fuel offset, will the "distance traveled" slowly fix itself? Or does that only take into account the speed offset?

If not, I guess I'll have to live with the 1km/h difference.

[keanucosmo]

I don't know if this is relevant here, but for my Corvette there was a TSB on this type of problem. I found this because there was a difference between the speedometer and the speed displayed digitally when I set cruise control.

Quote »The speedometers used on most GM vehicles are of the air-core design. This is a moving needle operated by a magnetic coil. Because there is no direct mechanical linkage, there is some variation in accuracy that cannot be eliminated.

Digital readout devices, such as some speedometer displays and HUD's (Head-Up Displays), are direct readouts of the VSS (Vehicle Speed Sensor) and their accuracy is much greater. Tire size, tread life and inflation can cause some variation in the readings. In addition, the Tech 2 device reads the VSS directly and is quite accurate.

It also showed allowable variances of

MPH/Variation 20/4mph 45/3mph 65/2mph[/quote]I know on my Versa when the speedometer shows 70 the gps shows 68 or 69.

I would think the ScanGage is reading the VSS directly via OBDII. I would try 0% offset