You ran an email on the usefulness and accuracy of official fuel economy figures, and mentioned you were adding the ability to log real life fuel consumption figures on your website. Like some of your correspondents, I too keep a log of my fuel use so I can track my business costs and have done for years. I have attached two extracts from my spreadsheet, showing my fuel purchases and mpg calculations over five years in an Audi A6 2.7tdi SE multi-tronic. Much of my driving is long motorway runs with some local driving. The car is standard spec on standard 17-inch wheels. The official combined figure for the car is just over 40mpg and in five years my average has been 38.5mpg, so it's not far off. My driving style is brisk but responsible.

The graph is interesting as you can clearly see the impact of cold weather driving on winter diesel, which I found in this car reduced mpg figures by 2mpg every winter. I show three figures, instantaneous mpg, i.e. for that particular tankful; the average for five tanks which smooths out the fluctuations in the graph making it easier to see a trend; and the long term average which just adds up all the fuel bought over the miles driven during the life of the car. I follow your refuelling technique when filling up. I did the same for my previous A6 and found the long term average to be almost exactly the published combined figure of 40 mpg.