ACCURATE WEIGHT?
When I was a line Captain on (big jet) with xxxx, I used to carry an extra 2000 kgs more than the CFP/NFP required to cater for known extra BURN on the regular 9 hour flight.All line pilots knew this, and did this, because we knew that inspite of best intentions at this very professional outfit, the ZFW was always understated, mainly from the Nigerian PAX who carried massive amounts of cabin bags.
When the fleet CP harrassed me about this practice, I told him if you look at the FMC target thrust in cruise, it is much lower that ACTUAL THRUST, meaning we are heavier than we think.To work out how much heavier, just keep increasing the ZFW number on your performance page until the ACTUAL THRUST and the TARGET THRUST are the same.The result is scary.All your V speeds are thus too low for take off and landing.
Funny thing was, the same CP had an engine failure at 500 feet agl from the same airport on the same route and couldnt climb away, in fact his bigjet started to descend!!! Eventually he managed it, but upon landing a re-weigh indicated they were 6000 kgs over the stated ZFW, so I have to take most of the comments posted here with a large pinch of salt.....Pete.