Our 742's and 744's don't utilize the aircraft system for calculations. It's done on a lap-top using shipping information, with weighing done where necessary or applicable.
Weight and balance is calculated in the 747 the same way it's calculated in a Cessna 172. In our case, however, we only need enter the numbers in specific places in a dedicated computer program, to get the totals. It's a lot easier when shifting the load around or making changes, than to work it out by hand.