Thanks once again to a remarkably tolerant "image" server, I have put up an excel spreadsheet with a pretty obvious bodge on the filename. Right-click and "save as" and just cut off the .jpg ending of the filename.

http://images.channeladvisor.com/Sell/SSPr...imeCalc.xls.jpg

If you ever wondered how long it would take for a modification to your car (or even a new car purchase) to pay for itself, strictly in terms of fuel costs, use this calculator. Gasoline is cheap and the moral of the story is generally "do it because you want to, not because you will save on gasoline money" but it's free and fun to play with the numbers.