A method includes moving a wafer transport device on a transport rail, wherein the wafer transport device comprises a hoist unit configured to grip a wafer container unit; stopping the wafer transport device above a load port; after stopping the wafer transport device, reading data of a rail mark located on the transport rail; aligning an orientation of the wafer transport device according to the data of the rail mark; after aligning the orientation of the wafer transport device according to the data of the rail mark, aligning the wafer transport device with respect to a top surface of the load port; after aligning the wafer transport device with respect to the top surface of the load port, lowering the hoist unit.