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Suppose you drive 5 miles at 247 mi/kwh. You used 0.02 kWh and the bar chart reads 247. Then you drive 5 miles at 3 mi/kwh. This uses 1.67 kWh and the bar chart reads 3. The average of the two bar readings is what GM is calling "Average energy consumption". That is 125 mi/kwh. Nice number. But gigantically wrong. The truth is about 6 mi/kwh. To quote someone on the other thread: "a bonehead error".

Details: 1.67 + 0.02 = 1.69 kWh; distance is 10 miles. The mileage rate is 10 mi / 1.69 kwh = 5.9 mi/kwh.

The error here is about 2000%. If someone is trying to maintain, say, a rate of 4, knowledge of this average is important. The bar chart is not helping. The red line is wrong. And the impression given by the bars is very misleading.

If you were driving very steadily, with bars between 3.9 and 4.1, the error would be less. I live in the mountains of Colorado, where steady use is never possible.

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I am trying to communicate this to GM, but so far the support staff I have contacted just say "energy use can vary", "it is just an approximation". I am trying to reach someone who understands arithmetic. I have prepared some notes on this -- they discuss this point, and also another interesting point about the difference between using miles per kWh (the USA way) and kwh/mile (the Euro and Canadian way, tho of course they use 100 km, not miles). I posted them at

<< stanwagon.com/public/BoltFuelConsumptionComputation.pdf >>

Digression: I actually favor the US Customary Units over the metric system, but that is not at all the point under discussion here. What the Europeans do in the particular realm of energy consumption ratios is far superior.

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There are other side issues, that are less important, but not negligible. If one goes down a long hill and gains kWh over a 5-mile stretch, the bar chart should show a negative number. But the programmer replaced any negative number (also any number larger than 252) by +252. The fact that negative energy exists is the whole point of a regeneration system. You would think that users could handle the concept. But clearly the designers did not think so, and chose to avoid negative numbers. I don't have a problem with that. I do have a problem with their saying that 125 is a reasonable approximation to 6.

If anyone knows someone who might know someone at GM who would care about this, do tell. It would seem like a very simple fix in the program to get it right. Just divide before taking the average, and then divide once more.

I can't upload my notes here directly because there is a very sharp limit of 20 KB (???) on file size.