LOL...okay..all this discussion is very interesting. So here I go. This is what I learn after being a Loadsheeter/Loadmaster/Flight Dispatcher.
DOW = Dry Operating Weight (Weight of the Aircraft/Crew/Pantry..etc..etc..But this depends also on the airlines requirement what they consider as DOW.)
+ cargo + pax + baggage + ULD's (some airlines use this as part of DOW)
ZFW = Zero Fuel Weight. (+ Block Fuel / RAMP Fuel)
= RAMP Weight (- Taxi Fuel)
= Takeoff Weight (TOW) (- Trip Fuel)
= Landing Weight (LDW)
MZFW = Maximum Zero Fuel Weight. The structural limit of the aircraft can handle.
Variable ZFW = This is usually meant for freighter aircraft like B742 or B744. What it does is basically allow the aircraft to carry more weight than the MZFW but the MTOW is greatly reduced.
MTXW = Maximum Taxi Weight
MTOW = Maximum Takeoff Weight
RTOW = Regulated/Restricted Takeoff Weight (if there is a restriction the TOW cannot exceed this weight)
MLDW = Maximum Landing Weight.
All these weights calculated in the 'loadsheet' cannot exceed these figures at any given point.
As for why plot it in the trim chart, well its to see if the weights and the position of cargo/baggage/passenger loaded in the aircraft actually 'balance' the aircraft out. As aircraft has 'curve' each weights has its own limitation hence its to ensure that both weights and the 'balance' of the aircraft is in the safety limits. Like freighter aircraft, the trim checks is to prevent 'tail-tipping' of the aircraft itself. Also, the pilots can use it for FMC for the whole flight.
