The relationship between bong and tan movements is inseparable, in that they are key to each other. Each exist in unity with the other, this it down to the axis of rotation for each movement and the shape they both share. Just by rotating the wrist in the centreline from bong sao, the tan sao is created. However it is the connection to the hip on both of these that truly gives both of these real and proper power. When executing a tan da (tan sao punch) the hip on the side of the tan movement is retracting, allowing the punch to extend and add power through the waist/hip. When that same tan movement is then put under pressure the relative hip then moves forward as the wrist rotates allowing the elbow of the bong movement to take the centreline.