Hi. I fly airbus and the Flight Augmentation Computers (FACs) use AoA sensors to calculate the aircraft Gross Weight. We had a problem two days ago on a four sector flight where the gross weight the FACs came up with was tonnes different than what we had entered in the MCDU. We knew the FACs were wrong just by pax numbers and cargo (we had no cargo). Yet both FACs agreed. Because of this our characteristic speeds were all way out (up to 20kts). Apparently if the AOA senser is just .3 of a degree out it can create 3000kg difference.