I assume there is high accuracy, well within 1% on the gas pump, and the odometer. Actually, I think the fuel injection pressure and timing (which determines volume) is very accurate, but due to the very large number of very small measurements that vary quite a bit over engine RPM and throttle demand, I would expect cumulative rounding errors to be a problem. That is, I am impressed that it is done so well from such difficult (sensitive) inputs.

-- Alan

 

I believe the display has a sampling error, which manifests itself more in stop-and-go traffic. When I do one long highway run, in my Prius, to the beach and back, my display matches the calculated MPG to within .2 MPG. When I drive a mixture of suburban and highway traffic, with lots of speed changes, the display is always 2-3 MPG higher than the calculated MPG.

 

The meters are regulated by the state board of ???? (don't know the official title). I don't know how frequently, but they are checked for accuracy. Also if a consumer reports that they think the pump is off they will check it out. I had that happen to me. My tank was 1/4 full and could hold 16 gallons. The pump was pumping extremely slowly and read 15.1 gallons upon filling up. I called the bureau listed on the pump. They went out, checked it and reported it as inaccurate. Don't know if the station was fined or just had to fix it, but I'm reasonably sure that the pumps are generally very accurate.

 

I remember reading a story about one gas station that had installed a modified control chip. It would always pump 5 gallons accurately but after that start cheating the customer. People would complain but whenever the pump was tested it always showed accurate because they used a 5 gal test. Finally after testing a number of times because they were getting so many complaints, they used a non standard test amount, found the descrepancy and from there nabbed them on the modified control chip.

 

Realjuice,
Was this your first fillup? Did you remember to subtract the miles the car had when you drove it off the lot from the total odometer reading. I ask because the first time I computed my mileage I forgot to do so. I too thought my actual mileage was better than the computer. Only after I realized my mistake did i come up with an accurate reading. Once corrected, my first tank average as computed by me was 38.4. The car said 39. It wasn't too far off.

 

Get a life. You've obviously decided to buy the TCH; now enjoy driving it.

 

Just did my second fill-up, but my first where I filled up at the beginning and end of the tank (dealer filled up first tank). The TCH indicated 36.8 mpg and I manually calculated 38.4 mpg. We'll have to see after several more tanks.

BTW, I went from June 19 until July 12 between fill-ups. I went away on vacation for a week, but it's still not too shabby.

 

After three tanks, I can say my mpg readings are roughly 1 mpg on the high side.

1st tank read 43.0 and calculated 41.7
2nd tank read 44.1 and calculated 43.3
3rd tank read 43.5 and calculated 42.2

 

I've also found the FE readings to be quite accurate, less than 1mpg on the high side over two tanks. In metric, so converted:

Both tanks finished with a reading of 38.5 mpg (6.1L/100km), manual calc was 38.0mpg and 38.2mpg.

 

As long as each trip is over 35 MPG, I'm happy. How whacked is this: I get all warm and fuzzy when my car says "EXCELLENT!"

...and you all know what I'm talking about, don't you?