RCSA,
Thank you for your comment.
I mentioned "Precision" in #54...
In smoother conditions the Captain might leave me hand-flying and walk to the toilet. Some of our toilets were near the tail of the York (others just aft of the F/D). We carried 40 passengers in "4 across rearward seating" ie. 10 rows. The York responded to this alteration of C of G by increasing the indicated airspeed speed by 1 or 2 kts, if I maintained my correct cruising level. When the Captain returned, the speed soon reverted to the 160 - 165 kts that it had been.
RVSM and wider cabins with 6 or more seats across and security makes this effect harder to observe. ( Captains weigh a smaller percentage of an aircraft's A.U.W. !)
LT