The “merry-go-round” used by children in the park is a simple analogy. Suppose the merry-go-round is spinning, and two children simultaneously jump off. In that case, one from each side of its diameter will be thrown in one direction and the other in the opposite direction. Similarly, when the Wing Chun man performs a stance pivoting Tan Da, both his Tan Sau and his punch “jump off the merry-go-round” simultaneously. However, the Tan Sau will go in one direction (toward the Self-Centerline), and the energy will go in another (into the Centerline).
The student is introduced to the concept of “Reference,” which in its most basic context refers to the focus of an individual moving to a given point in space through a combination of certain Siu Leem Tau and Chum Kiu motions and the logic behind them. When the student first learns the Syeung Kuen (Double Punch) motion in the Siu Leem Tau form, he is taught to strike vertically with both sets of knuckles on the Original Centerline rather than with one fist stacked directly over the other. This leads to the realization that, even in a single punch, the “reference” to the Centerline should be the knuckle points rather than the middle of the fist. Although a hole is a Yang motion, the knuckles refer to the Self-Centerline because there is no stance pivot in the Siu Leem Tau form. Tan Sau and Woo Sau, as well as other Yang motions like Boang Sau and Jing Jyeung, fall into this category. The Centerline and Self-Centerline do not separate until the Choh Ma stance pivot in the Chum Kiu form, with the Tan and Woo remaining reference to the body and the punch remaining on the original Centerline.
Pock Sau, without a stance pivot, and again when pivoted, concerning the Centerline. Although the stance is not shifted, the Pock Sau slap block in the Siu Leem Tau form (photos A and B) references the past Center, subtly introducing the student to the principle of focusing Yang blocks to the Centerline when they are eventually executed with a stance pivot. This becomes clearer when Pock Sau is seen from above pivoted. Its body structure remains unchanged, with its reference fixed on the Original Centerline.
The Pock Sau slap block motion in Siu Leem Tau laid the groundwork for this concept; the Pock Sau motion originates at the Centerline and moves inward and forward past the line when executed in the form. However, the application focuses on the Centerline while maintaining the same relationship with the body as its non-pivoted form. When students understand the fundamental concept of reference, they can begin to execute the Siu Leem Tau techniques previously practiced in the stationary “Yee” Jee Keem Yeung Ma position, with various other forms of footwork beneath them. For example, the same straight punch described above could be carried out with Choh Ma footwork, which adds torque and slightly changes the angle of the point but does not change the reference.
In other words, when you turn with a punch, the knuckles of the punching hand should land precisely where they would have if you hadn’t pivoted, except for a slight increase in the length of the punch. If you swing and punch again on the opposite side, the knuckles of the opposite hand will occupy the same point in space. The pivoting effectiveness at the start of the Chum Kiu form introduces this to the Wing Chun student. Except for the pivoted stance, this punch is identical to the first punch of the Siu Leem Tau form. Its reference point (the Centerline) remains the same. However, the body now faces 45° outward, and the punch becomes slightly longer and more powerful. The Choh Ma Boang Sau motion also introduced the concept of Yang blocks remaining referenced to the Centerline even when pivoted in the Chum Kiu form. When you practice the form in front of a mirror, you will notice that you are being shown to block the same punch thrown earlier in the state with a Yang block focused on the same point in space as that punch.
The Choh Ma Lon Sau demonstrates how a Yin block remains referenced to your own body, as it did in Siu Leem Tau. In contrast, Yang motions such as the punch and the Boang Sau remain referenced to the same point on the floor that they did in Siu Leem Tau. As a result, the Chum Kiu level student will realize that the Centerline viewed at Siu Leem Tau level was made up of two lines that happened to overlap because you were pivoted to the exact Center. However, as you began to shift, you noticed that the line splits into two—the one that remains “painted” on your body (the Self-Centerline) and moves with you as you move, and the one that remains “painted” on the floor (the Centerline).