Hi Duncan, I'm a n00b from just across the river in Aus and born in NZ (christchurch).
Good to see someone else in our hemisphere on here.
Here in Aus people are still a bit stupid about fuel I think... every 2nd car is a V8 and we complain about paying AU$1.70/L, I believe you guys are over NZ$2/L now?
As for your conversion dilemma, the great god Google has us covered, you can simply key in your 'equation' as a search, such as "540km/60L in mpg":
http://www.google.com.au/search?hl=e...m%2F60L+in+mpg
And Google will tell you:
"(540 km) / (60 L) = 21.1693125 miles per gallon"
I don't know if that is US or UK gallon, changing the google locale (using google.com instead of .com.au) doesn't seem to have any effect.
21mpg seems more reasonable than 16mpg (edit: ignore that, I read your spreadsheet wrong) for a falcon though... surely our cars are not _that_ bad? hahah.