It all depends if you believe the standard passenger weights, bags that are offloaded from the cabin suddenly going from weightless to 13kg. Etc etc etc.
There are a lot of unknown variables in the W&B that are not accounted for, 100kg of Fuel isn't going to do anything in an A320-sized aircraft. Offcourse try to get it as accurate as possible, but it's not an exact science. You would need to weigh every aircraft to achieve this. Then we also guesstimate the taxifuel in order to reach a guessed TOW. So lets keep some perspective.
With regard to the fuel panel on A320, it varies per aircraft. The 3 clicks will add 100kg, but the panel will show the same number for all 3. So say you want 6.7 I usually go until I see 6.8 and then go 1-click down in order to get 6.7 on the display. This will usually give around 6740 in the tanks, but sometimes less then 6700. A bit random per aircraft and even per refuelling. Also changing the number midfuel seems to sometimes mess things up.
Our digital w&b module alteady does a lot of rounding. Weightare determined to the nearest (highest) 100kg. So we see something like 68.6, no idea if that is 68.549 or 68.600
However on a small turboprop, a 100kg can be a major difference.
Last edited by 737Jock; 24th Apr 2013 at 16:32.