Tan sao, or "Palm-up Arm," is one of the three core movements of Wing Tsun/Wing Chun chi sao. A defensive technique, it involves rotating the wrist so that the palm faces upwards. The forearm is used to guide the opponent's attacks away from the body. Position of the elbow is very important, but differs with purpose. For instance, the "sideling tan sao" points the elbow outwards, while the fingers of the hand point at the opponent's center line.
In contrast, the tan sao utilized in chi sao places the elbow at the center of the body, while the forearm points away from the body at about a forty-five degree angle.
Tan sao is a very versatile principle. In fact, history records that one Wing Chun practitioner was even nicknamed "Tan Sao" because of his skill with and affection for this movement. Tan sao and bong sao are intimately linked. The transition between the two movements is responsible for the rolling motions characteristic of poon sao and, later, full-on chi sao.
Like the other core movements (bong sao, pak sao, fuk sao, etc.), tan sao is learned very early but never outgrown. In fact, it is an integral part of the fourth and final Wooden Dummy Form. Unlike bong sao, it has no offensive application, but transitions very easily into the devastating palm strikes, spade hands and darting fingers of Bui Tse, the third form. | 
