Ever changed your fuel log readings?
 

... after recalibration. I have never changed my numbers. I always report what the PUMP/ODO calculation reveals as FE. I do not rely on my Ultra Gauge. I do this because I have been confident that my ODO is better calibrated, even though I am sure it is not perfectly precise. But using google maps to calibrate the ODO I have found indications that it might be off by 0.2-0.4%. In a couple weeks I will test it using a longer, flatter google maps identified route, with no EOC. If you found, through such a test, that your ODO had been off, would you adjust your past and future ODO/PUMP FE calculations to correct the deviation?

I haven't edited my fuel log, but I've thought about it. I know my current tires are off a bit from the standard size( around 1.3% by buyer guide, if I remember correctly), but as this is only point of reference for improvements, I just go by ODO readings. At 260,000 miles plus, it wouldn't surprise me if it is a bit off.

In the past I always used my car's odometer to measure mileage.

Early in 2011 I got an MPGuino, and in April competed in the 2011 Green Grand Prix (GGP). Planning for that event, I borrowed a GPS so I could calibrate the MPGuino as precisely as possible. I had about a 300 mile drive up to the GGP which gave me plenty mileage to compare the trip odometer with the GPS. I dialed in the MPGuino so it was now very closely matched to the GPS data, and subsequent driving with the GPS showed that calibration to be consistent.

Once I had the MPGuino calibrated from the GPS, I used the Guino distance for my fuel log. I think the carefully calibrated Guino data is more accurate than the car's odometer. Just my opinion.

From the point where I first calibrated the MPGuino based on the GPS, I used the Guino numbers in my gas log. When I later changed tires I tested it again and made an adjustment to the Guino setting to match the other tires.

A question I have is... once calibrated how long would the UG mileage gauge become. Because when I calibrate it now I see variation tank to tank as to how close to spot-on it is relative to the ODO. Maybe EOC messes with the UG's numbers a little, on the margins. Probably the only answer is an MPGuino, huh?

(Sorry - I haven't used an UltraGauge so I don't have specifics on that. But I think the fuel + distance input data are distinct for UG, just that the fuel input is from a different source than with the MPGuino.)

I've been considering as separate, the MPGuino calibrations of distance and fuel quantity.

The distance calibration should be pretty consistent, I would think - actual distance would decrease slowly as the tires wear down. So far I've calibrated the MPGuino by GPS before each annual Green Grand Prix so I think that's good enough. I do use the Guino distance readings for my fuel log.

I found that fuel quantity accuracy seemed pretty consistent - until I did some minor injector maintenance (notes below). Prior to that, the MPGuino "measurement" of gallons used was generally within +/- 0.1 gallon of the actual that I pumped. That was as long as I used the same pump, same station, same fill method. For me, that's a 2/3 squeeze until about 1 gallon before anticipated click-off. Then 3 seconds per 1/10 gallon until it clicks off. That's pretty darn slow, and seems to fill it nearly to the top of the filler neck.

About a month ago I decided to run some Seafoam through the gas tank. I included the Seafoam qty in my fuel consumption. Since then, the car takes slightly more gas when filling than the MPGuino estimate. I'm theorizing that the Seafoam cleaned some crud from the injectors, which now squirt just a tiny bit more fuel per microsecond that they are pulsed open. I'm still accumulating notes on this apparent fuel increase so I can dial in a correction in the MPGuino. HOWEVER this deviation doesn't affect my gas log or the Team Competition, because I always record the pump gallons data in the gas log. I just record the MPGuino "estimate" fuel in the notes, for use later in calibrating a correction for the MPGuino. I don't record the Guino estimate if I have to fill at another station or if there is anything else that would make the fill "atypical".

I put 20k miles in my fuel log, assuming my OEM tires and odometer were accurate. Then I bought taller tires. In the course of testing them, I calibrated them during a long drive to Southern CA. The odometer readings with the new tires were 9.9% pessimistic. 100 miles on the odometer was actually 109.9 miles traveled. I checked this over 20, 60, and 80 mile distances.

When I got back from that trip, I checked my OEM tires, and found the odometer was also pessimistic with them: 100 miles on the odometer was 103 miles traveled. Yes, I went back and redid my mileage log(s).

Both UG & SG lose miles during the key off/ECU reboot entering EOC. If I drive my 10 mile test loop with cruise control, and then do the same drive with EOC P&G, I'll see a .3 to .4 mile shorter trip distance with UG or SG doing EOC with the key. If I do it with a kill button, the trip distance is the same as with cruise control.