True enough there's a few things that we don't really know, for example the exact seating positions of the hundreds of people and the average CG for them, and the same for the containers, eg, "There's four in the front and six in the back"
As you no doubt know the room under the floor of the 747's means that those ten containers could be moved around a fair bit!
But to give you an example of how far off the computer one can be, I calculated the stab trim to be 4.5 units (which we used) and the computer came up with 6.5.
I specifically took notice on take-off, and the controls felt pretty good to me. With 6.5 units, it would have been way to light and very nose-up.
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Motion coming on!