Very cool info man.
some additions and notes
* ambient temperature
* barometric pressure
* vehicle temperature (not just engine, but the entire drivetrain including tires)
* fuel grade/quality
* elevation/road grade
* road surface conditions / type
* other traffic
* driving style / driver psychology
almost all of this stuff with reasonable caution is MINOR in the bigger picture.
Example look at my fuel economy history for ryo-ohki it really does not deviate a whole lot from day to day. in fact is usually does not deviate more than 1mpg overall.
what is needed is LOTS AND LOTS AND LOTS AND LOTS AND LOTS AND LOTS and ... just a few more Runs again and again.
the more data points you have the more irrelevant small variables are.
even a 40' change in air temperature is NOT going to alter your fuel economy at all. Yes technically it will but not enough that ANY of us likely has the equipment to measure off a dyno :-)
so just make lots and lots of runs. through out the higher and low points and average the data.
lets say you make 20 runs and most are 47mpg 2 are 49 and 50 and 3 are 45 44
well toss out the 45 44 runs and the 49 50 runs average the rest.
for the purposes of deciding if more energy into a project is WORTHWHILE or not this is more than accurate enough data to come to some sort of conclusion.
While this info is VERY important for us when BUYING improvements for the community its just not needed
99% of us WANT to see improvement in our MPG and we will work to that goal 100% of the time a b or a. IE when your offering up info USUALLY the person has no reason to decieve or burn people and they have nothing to sell you so they have little to gain (there is of course always that 1% who just like being dicks :-)
when you make your A B A runs just make sure you do 20+ runs for A and 20+ runs for B and then just enough for the last A to confirm the results.
that should be more than enough data points to average out outside variables if your reasonably cautious and careful.
now there is one thing that IS a huge variable that used to NOT be a huge variable.
FUEL. in over a million driven miles I saw ZERO difference that could not be argued away as noise between gas at one station and gas at another station.
lately though with the introduction of ethanol I have seen MASSIVE huge swings in results from fuel. as much as 8mpg from one station to another. since I started ONLY buying gasoline at Wawa Gas stations (the lowest ethanol content and consistent so far) my fuel economy has settled down and gotten a LOT more consistent again.