However, a "typical" consumption line is plotted on the energy meter at 311 Wh/mi. This could be the figure that
@arg is quoting.
Well, there's a line a couple of pixels up from "300", so it might be at 311, but I can't read it to any real accuracy. However, a number somewhere around there matches up with my experience.
I haven't monitored this really closely since the software update that introduced the trip energy graph - nowadays that's always what I use for any trip where range is demanding. However, when I first had the car and that feature wasn't in the software (and also there were hardly any superchargers), the standard thing to do on any trip was to watch miles-to-destination on the nav, subtract that from available range on the fuel gauge to give a margin figure, and keep checking the margin every few minutes to see if you were gaining or losing relative to Typical range. I have a note from back in that era when I started with 214 miles on the gauge, drove 208.3 miles at a displayed 290Wh/mile; unfortunately I didn't record how many miles I had left when I got home, but it was probably about 20 - so I was getting better than Typical range at 290Wh/mile. Conversely, at normal "trying to do 70mph" sort of motorway driving in summer I get about 330Wh/mile and get a bit less than Typical range. So for my car 311 is very believable.
It also roughly matches the capacity calculation: my "85" battery gave 245 miles at 100% when new, and is reputed to have 77.5kWh usable, which would give 316 Wh/mile.
It's possible things have been screwed up in recent software, though I don't think so. As it happens, I had a very tight journey a couple of weeks ago (for the first time in ages!), though unfortunately I didn't know it was going to be controversial so I didn't take notes - all I can say now is that the numbers on the screen all matched my expectations. I was at Stonehenge with 50-something typical on the gauge and 48 miles to run to Fleet supercharger. The Nav told me I would have 3% at destination. I set off in queuing traffic and it dropped to 2%. I then hypermiled vigorously over the 10 miles to the decision point for diverting to the Geniepoint charger at Thruxton and got it up to 5% so carried on (low 200's Wh/mile); by the time of deciding to skip Sutton Scotney I was over 6% and driving slightly faster; once on the M3 it was obvious I was going to make it so was doing 70mph. Can't remember exactly how many miles I arrived with, but it would have been pretty much dead-on typical range for the journey.
Obviously your S70 will be slightly more efficient than my S85 (more so if yours is a S70D), so I'd expect a slightly lower figure maybe 286 is right for you. OTOH
@thegruf 's P100D is supposed to be significantly worse than yours and maybe even worse than mine, so 235 isn't plausible there.
I'm not sure how many versions of "Typical" there are - if it's just three numbers for RWD/D/PxxD, or if it's been calculated for individual models, or even things like the wheel size (IIRC, the car knows what size wheels it is supposed to have fitted).
There's always been some kind of fudge-factor involved in the range calculation, as they have always tried to guarantee it will never run out before zero (ie. any uncertainty in the range estimation is put on the negative side). In the earliest software (before I got my car) it seemed to be very crude - the starting range after charging would be estimated with one Wh/mile value, then as you drove it would decrement based on actual Wh used at a higher Wh/mile, and people would often report driving long distances after the display reached zero. More recent software has blended this better (and is probably much more accurate at making the capacity estimate in the first place). I think all the fudging goes into the displayed range number and the Wh used display is straightforwardly reporting the energy measured at the battery terminals, though the whole thing is always going to be an approximation - at a given state of charge, the total Wh you can draw out of it will be greater if you drive slowly than if you drive hard, since the harder driving gives a higher current and hence more energy wasted inside the battery than never makes it to the point where you are measuring at the terminals. And then again the whole thing is temperature sensitive.
