The process of loading luggage is a high-tech "ballet" that begins at the check-in counter. Once you drop your bag, it is tagged with a barcode (LPN) and sent through a maze of conveyor belts and security X-ray scanners. In the sorting area, automated sorters read the barcode and divert the bag to a specific "pier" for your flight. From there, ground handlers load the bags into Unit Load Devices (ULDs)—large metal containers shaped to fit the airplane's fuselage—or onto baggage carts for smaller "bulk-loaded" aircraft. A motorized "Belt Loader" or a "High-Loader" (for containers) then lifts the luggage to the cargo hold door. Inside the plane, "rampers" or automated rollers move the containers into place and lock them down to prevent shifting during flight. This entire system is designed to ensure the plane's "weight and balance" remains within safe limits for takeoff.