This could be very informative. Is it supposed to be an overall setting or can it refer to individual fills? I have often added notes to my fills when my driving for that period has had an unusual split between city and highway. I can certainly see the difference in MPG or L/km.
Cookie, you set the City % value on individual fuel-ups, and the graph on the page reports the average city/highway split across all fuel-ups. You also see the City % you entered in your fuel log on individual fuel-ups.
Digging the new stuff on the site. I am just logging all my coutry travel as highway since where I live you can pretty much just cruise backroads and only hit a stop sign or a town about every 20 miles.