I have a spreadsheet (yes I AM an engineer
).
13 Fillups so far -- Worst was 16.53 mpg.
Current average over 4000 miles is 21.89 mpg.
Actually started doing this with one of my previous cars. I was curious if I'd get different mpgs depending on where I filled up. Over a years time I filled up at different gas stations. I consistantly got lower gas mileage at one of them (don't remember the brand at this point, it was 10 years ago and I have since moved)