Quote:
Originally Posted by extrashaky
That's not the only assumption you're making. You are also assuming that the error doesn't change with the driver or the type of driving. It could be that these things are exactly accurate for certain drivers and way off for others.
There is also a geographical element. People in different parts of the country are using different fuels. For example, it could be that the computer was calibrated using fuels available in California during the summer months, and during all other times of the year and in different locations the additive package throws off the calculation. You also have the problem that some people live in relatively flat places (like me), while others live in mountainous areas. Altitude will also make a difference, since 91 octane at 5000 feet behaves like 93 octane at sea level.
To do this right, you'd have to control for as many of these variables as possible. Or control for the big ones and then try to explain the outliers.
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Ok, disregard my previous reply. I see where we disagree now. I am assuming that the error doesn't change from driver to driver, type of driving to another, fuel type to fuel type, or location to location, and you think this is a bad assumption. However, I think that this is a fair assumption. No one here has falsified this assumption; so far everyone has reported that their dash reads too high for mpg. I'm not saying there doesn't exist a person who's dash reads perfect or actually underestimates, but I don't know of one yet. It would help if I could find some information about how the BRZ calculates its mpg. Fuel type and driving conditions might not make a difference, maybe the computer just polls how much fuel is currently being consumed and how fast the vehicle is moving.
It will take a bigger experiment to figure out why the dash is reading higher than expected. Maybe the source of error is that the mpg measurements are made discretely and not often enough, resulting in an overestimated approximation. Sort of like approximating the area under a curve numerically and not using a small enough dx (change in x). The experiment I am performing now is to conclude with evidence that the dash reads higher than expected.