Many, many years ago, when I was but a puppy, I used to do loadsheets and the APS weight was the weight of the aircraft with all the galley stuff, pilots and hosties but no load, i.e. an empty "Aircraft Prepared for Service", with just the FRT,SLF and fuel to pour in. We'd start with an APS weight and then add the load to get a Zero Fuel Weight (probaly all called "mass" now in this PC, Eurocentric world) and then subtract that from the MTOW to get a max fuel load and hope it got us there! (No, seriously we weren't really that gash).
I remember asking to put a car on an empty leg from Lye to sonewhere in the UK and asking how much it would add to the burn and all and sundry said negligable but it was only a Nissan estate so I don't think it was 2.5MT.
Do I remember wrong?
Doc C