Dashboard Calculator Not Trustworthy.
Left work one AM, showed '65 miles until empty' on computer. Drove 14 miles to work. Left work that afternoon, computer said '34 miles until empty' (Hmmmmmmm 65-14 = 34? Must be new math!). Drove 1/2 mile to Freeway on-ramp and computer changed to "EMPTY". Ended up having to find a gas station and paying appx .20/gallon higher than prevailing (didn't want to risk that computer was actually teling the truth) Park in underground garage: can't attribute issue to Heat/sunlight.
I have an XG300 - the computer bases its reading on how you're currently driving - speed and current fuel use vs. fuel remaining in tank. It can only give you a rough estimate. I also find that it's more accurate once you get below 1/2 tank. The number will keep changing - sit in traffic and it'll say "100 to empty". Pull onto the highway and after about 5 miles it'll say "110 to empty" - you've driven five miles but gained 10 miles worth of gas because you're moving. If you want to use it as an accurate gauge, then you better carry a gas can.
I have an '02 XG350. The computer always goes to EMPTY after "32 Miles to Empty". So count that as your zero point. If you have 62 miles to empty on the computer then you actually only have 30.