Late model ford question

Hey I gotta question for you guys that know more about late model stuff. I have a 04 mercury mountaineer with a 4.6 it has one of the oil change percentage calculators in the dash, no matter what it always says oil change required! I can change the oil right now reset it to 100 percent and drive it half a mile it immediately pops up and says oil change required again. What controls this and how do I fix it?