This is a pen that relies on a special refill, internal structure and magnetic metal counterweight ring to achieve a customized weight and center of gravity. It has an appearance structure that conforms to the habit of holding a pen by hand. It can realize that a pen can have various hand feelings such as pens and ordinary sign pens, and is suitable for various writing scenes (writing, painting, calligraphy ......). Reasonable use of center of gravity transformation can reduce hand pressure and bring the best writing experience