Treatise on Armament Technology, Volume 102: Crossbows, Part 3

Explanation of the Sparrowhawk Staves

Historically, crossbow limbs referred to here as dan (擔), the staves or "yokes" that form the bow were constructed by joining two pieces. While the center of such a bow remains stiff and powerful, the two tips inevitably remain weak; consequently, the arrows cannot be discharged over long distances.

In this new system, three pieces are joined at the center. By making the fourth, fifth, and sixth staves progressively longer, the power at the center and the power at the tips are rendered balanced and harmonious.

The first, second, and third staves utilize the original thickness of the bamboo. In this design, at the center section—spanning approximately six cun about 19.2 centimeters—half of the thickness is shaved away while the other half is retained. These staves are then inserted into the limb socket original: dan yan (擔眼); literally "stave eye," the mortise in the crossbow stock where the limbs are secured. This allows the center to sit lower while the two tips are angled upward. When the bow is strung, the curvature resembles the shape of a sparrowhawk's wings spread in flight; hence, it is given this name.

The fifth limb stave is 1 chi... The text continues the measurements from the previous page, detailing the remaining laminates for the Sparrowhawk assembly.