when you unload, do u have a person who follows you to your door and takes all your packages on seperate belts? that is your sorter, they know the primary sort test. That is the first time they are sorted (hence primary). After that it travels to the PD's and the pick-offs, those people know the secondary sorts for what box goes to which truck etc.... the primary is pretty easy if your good with numbers and colors, or good with maps and colors. for instance in my hub every west of the mississippi river (including the state) goes to one belt, while texas, Parts of Cali, and all the states from nebraska north to north dakota go to other belts. you would have to know which belt for which box etc. its really easier than it looks, once u get the hang of it, its like second nature.