Forget that fuel log book – switch to storing that info online – much more powerful and convenient
Yes, I used to log all my fuel fill ups in the log book and manually work out my fuel consumption and try to spot that increase in fuel consumption to alert me to something going wrong in the engine compartment�. Wow, that�s a mouthful, and so was doing it manually.
The schlep of finding a pen and filling in the details, then remembering to calculate the fuel consumption per Km � is it litres divided by km or the other way around�. Ummm, well I don�t really care anymore � I switched to a web based app that calculates all that for you.
Fuelly: It draws charts on consumption and you can even compare your consumption with similar vehicles all over the world. There are also fuel saving tips. All of this for free! Register and start using it now.
All you need to do is remember to enter 1) Kms since last fuel up; and 2) Litres of fuel purchased; Optional info to enter: Price/Litre, notes, tags.
It will then immediately show you the last tank�s fuel consumption statistics: 
The user interface is configurable to use metric or US or UK or L/100km or Km/L, and currency (eg: Rands)
The overall historical statistics is shown using a customisable dashboard: 
Also some nice charting to show your statistics over time: 
It even gives you that (old fashioned) log book view: 
The �Fuelly Mobile:� URL is a lean and fast way to enter those fuel-ups at the petrol station: http://m.fuelly.com
I have stored a bookmark in my phone to jump directly to my car�s fuel-up page.
And a bookmark in my wife�s phone to jump to her car.
See here for videos on how to use Fuelly: http://www.fuelly.com/about
Importing and exporting of your data is also possible.
Follow them on Twitter here: @fuelly