The Nautilus Rotary Neck Machine contains no weight stack, no built in source of resistance of any kind ... instead, the resistance is provided by the user through the use of hand levers that enable you to exactly control the resistance during both the positive and negative parts of the exercise. There aren't many Rotary Neck Machines around but we happen to have one in our private gym and when used correctly, it is excellent. We may do a feature on it at some point.