Depending on the number of wheels, the weighing might have to be done in pairs of wheels. For example, each nose wheel would go onto a separate scale. Pairs of main wheels (side by side pairs, that is, not fore and aft) would be weighed together. It can be a long process. The weights exerted by each separate wheel are added to give a total weight. The weighing of a large aircraft is usually done with no fuel in the tanks.
