I always fill until I see the diesel foaming up to the neck, wait 5-6 seconds, then fill until the cutoff. It's not a 'calibrated' fill but it's pretty accurate, and, thanks to my anlly retentive mindset, I use a spreadsheet to record each tankful, mpg, miles per litre, cost per mile, cost of tankful, price per litre and average mpg and average price per gallon/litre since purchasing the car.
I also record the overall cost since date of purchase and year-to-date (plus cost per mile for each category) for depreciation, fuel, insurance, VED, finance + repairs/servicing. The spreadsheet also projects annual and weekly mileage for the current year from the year-to-date figures.
All of which probably explains my low annual mileage - I spend more time maintaining the spreadsheet than I do driving the bloody car :thumb:
So, up to today, I have owned the car for 57 weeks and have paid an average of ÂŁ1.19 per litre (lots of cheap French diesel!) or ÂŁ5,39 per gallon. Average mpg is 49.52 (includes a fair bit of towing/manoeuvering a trailer in '27 point turns' because of tight property access); solo driving between France and Scotland gives 48-52 mpg depending on how late I have left it to reach the ferry (we were last vehicle to be loaded on 17th December and had about 45 seconds to wait - not long enough to remove the headlamp deflectors :nod

.
Full year mileage 9777 gave VED 1p per mile, insurance 3p, repairs/servicing 1p, finance charges 2p, fuel 12p and depreciation a whopping 55p (based on writing off the entire purchase cost over 3 years. When I sell the car, I add back the sale price to recalculate the depreciation charge).
I'm quite an interesting person to know - especially if you wish to save yourself the cost of a trip to Dignitas - 20 minutes with my spreadsheet will do the same thing painlessly

).