The cam or chains in a loom makes the shedding lever rise & fall. Heald frames are attached to these levers which also rise & falls hence creating a shed through which the weft passes creating a weave. With reference to the cam design or chains the number of times the lever rises & falls and stays up or down with reference to picks creates a design as required. Hence levers are called shedding levers and is considered to be the pulmonary function of the machine.