How does FSX Flight Planner know how much fuel I'm going to use? How does it know it base its calculations? I wanted to know because I want to fly the Duke X-country and i want accurate fly plans, I wanted to know if anyone uses this planner and if the numbers it gives me are close to correct, thanks>

For the Duke I use the FSX Planner fuel estimation * 1.2 + 300 lbs.At cruise level I limit fuel flow to 170 lbs/h for each engine.Not very accurate but good enough. :( Alex