It's a rough estimate. Computer knows how much gas is in the tank and it makes an educated guess on how many miles you have left by your current MPG.
2012 Fusion Sport, 56k miles, White Platinum Tri-coat. Every option except nav. 28% tint, Diode Dynamics LEDs, Steeda CAI, Steeda 93 octane SCT Tune, Steeda 22.5mm RSB, Magnaflow Catback, Enkei Raijin
[SOLD]2004 SEL Premium, 72,700 miles, Vibrant White. 35% Tint, K&N Panel filter, Remote Start, 4x Infinity Reference 6832cf, JVC KW-R800BT, Rockford Fosgate 501bd, Bazooka BT1014
1989 Mustang LX 5.0 Vert, White, T5, built motor/driveline, race suspension, fast/loud as f*ck