A small, but important to know, update has just been released. Your movement fuel calculations now include mass adjustments that occur when your ship is performing an alchemy mission (Neutronic Refinery and Merlin) or when your ship is building fighters or torpedos. If you have your ship set to do one of these missions your overall mass will be adjusted before movement.  When you set your waypoint it now calculates this mass change in the fuel calculation. So your calculated mass is less and fuel consumption will be less if you are performing one of these missions.