Sorry mate I will try again. All of the centre tank fuel is used. There is no unusable fuel in the centre tank. As you are aware, when the fwd No. 1 fuel switch is on, the centre tank fuel scavenge jet pump operates automatically to transfer ANY remaining fuel to the No.1 tank. Transfer begins when the No. 1 tank is about half empty. Once the scavenge process begins it continues for the remainder of the flight whether there is fuel in there or not.