From the trajectory of the waist line of the human body, there will be a drop of 0.5 centimeters in the front and middle.

At this time, the side seam of the garment is outward inclined to the right angle.

If the outside of the seam is bigger, the rise and fall of the side seam will be larger.

If the amount of the positive side seam is large enough to make the side seam slanting yarn, it is necessary to increase the 0.5 to 1 centimeters on the basis of two lines at right angles. This is the way to solve the problem of elongation of skew yarn.