Sienna fuel display thing (the one near the inside mirror)

[touringcamry]

I was driving my parent's 04 Sienna from Los Angeles to Las Vegas (265 miles) and played with the computer fuel thing near the inside mirror. It has a setting that displays an estimated distance until the vehicle runs out of fuel.

How does this display work? The display did not agree with the miles driven on the trip meter on the dash. They were different by about 30% almost.

[Anshu]

remaining fuel x avg milage?
that would allow for the difference because all highway crusing