One of the key procedures for using a Kirby Vacuum is the correct way to adjust the carpet nozzle for the best possible results. Starting with the 1939 Model 2C to the most current machine, the instruction manual states that the carpet nozzle should be gradually lowered into position with the Toe-Touch control, incrementally adjusting the rug nozzle until the rotating brush bar establishes contact, and the sound of the motor changes indicating suction has been achieved. Starting with the 1945 Model 505, adjusting the carpet nozzle employs what Kirby calls "Triple Cushioned Vibration Rug Cleaning Action". This characteristic which is still implemented on current models, involves briefly lifting the carpet up off the floor with the significant suction created by the motor, thereby elevating and cushioning the area to be cleaned, while the rotating brush bar separates and grooms the carpet fibers, removing the embedded dirt and rejuvenating the carpet pile. One of the most common complaints about Kirbys is that they're heavy. The image of the machine made from metal adds to that reputation. The difficulty to push the machine is largely due to the suction created that makes it difficult to maneuver, especially in deep pile carpets and not necessarily the materials used in manufacture, however, for elderly users or users with arthritis, the 23 pound (10kg) weight can make it difficult to use.