My Roadster tells me, apparently with decent accuracy, how much range I have left. Both ideal range based on steady 55 mph without heater or A/C, and if I continue to drive the way I've been driving the last 30 miles. How does it know the actual number of kWh remaining in the pack? Presumably it's not just measuring the Wh used and subtracting from ideal full pack, because as the pack degrades with age the gauge knows. Does the pack voltage tell you how many kWh remain in the pack, even as the pack degrades with age? That would surprise me, given the level of precision it would need to detect the difference in pack voltage as remaining range declines by just a few miles. If not, what else can it measure to calculate this?