Laptops, cameras, loose change
On flights with many business travellers you also need to think about the extra weight of laptops, batteries, multiple phones, digital cameras, loose change in several currencies and so on. This is umpteen kilos of stuff per person that didn't exist twenty years ago. Beats me how the overhead bins don't collapse on people's heads during sporty landings.
And weighing hand baggage is a waste of time because seasoned travellers transfer all the heavy stuff to their pockets or hands until after the weigh in.
But they can weight loaded trucks just by driving them over a special bridge. Couldn't they equip the airport with something that actually weighs the loaded A/C? Wouldn't this avoid doing a lot of hard sums?