Never made a graph. Different kind of obsession... ;)
Last diesel I owned I kept a LOG with data on Amount of Diesel, Cost, Location, MPG, Mileage, Price, and location of purchase.
I tracked it all for 6 years. I quit when I sold it...
Haven't even thought about it with my current truck.
My tracking was pretty much a waste of time, but it was my time to waste.
I did determine that repeatedly one particular station near me gave me better MPG with their Diesel.
I determined that my Ford MPG meter reading was pretty much spot on.
I finally quit doing the math for MPG.
I determined my average MPG towing/not towing ect...
Mountains VS flat land Interstate driving.
I'M ALL BETTER NOW. GUESS I'M OVER THAT SICKNESS... ;)