As Andy says, the range figure on the trip computer is an estimate, based on the last 50kM of the journey. It is often optimistic, it depends on the accuracy of the tank level gauge, which is never very good. The trip computer is estimating how much fuel you have left based on the fuel gauge sender.
You can only claim a real range if you've actually driven it, start to finish, on one tank of fuel.
Have a look at your manual for a description of the various readings you can get from the trip computer, and
how to see them all. There are two sets of registers: one gets reset after a stop of a couple of hours, the other carries on accumulating trip info until manually reset. The button on the bottom of the stalk switches between the two with a short press. If you hold that button in, it resets whichever register set is being displayed. The short-term set, that resets automatically, is set 1, the long-term set is set 2. There's a little 1 or 2 displayed on the right hand side of the MFD to tell you which is being displayed.
The MFD displays the following parameters
- Outside temperature
- Time of day
- Driving time
- Average speed
- Distance covered
- Range (based on last 50km driving)
- Average fuel consumption (over distance since last reset: updated every 5 seconds)
- Current consumption (renewed every 2 seconds)
Cycle through by using the rocker switch on the end of the stalk.
The average consumption is measured over the distance since the last reset i.e. the distance in the "distance covered" display and updated every 5 seconds i.e. the trip computer takes another reading of the instantaneous consumption, checks the distance covered since last update and recalculates.
Range is based on the average consumption over the last 50 miles, divided into what the trip computer thinks is left in the tank. The tank gauge is the weak link.