"whatever clever people decide" is a (lazy) cop-out. You're just saying "the right answer is the right answer. Easy! Just do that, and do it yesterday!!" Thank

"whatever clever people decide" is a (lazy) cop-out. You're just saying "the right answer is the right answer. Easy! Just do that, and do it yesterday!!" Thanks Tautology Man. :-/ Acting like you're entitled to some (vaguely defined) perfect solution isn't a substantive technical discussion. If you don't know what you're even asking for (conjuring nebulous 'clever people' to fill in your blanks), then you don't know if it's even possible or not! There are lots of "good enough" range estimate solutions (long used on older cars), but there's no perfect solution that will never over-estimate the range ever ever ever (not ever). If you 'solve' this by making the range estimate wildly pessimistic, the driver will simply learn to mistrust-and-adjust, and then you're right back where you started.