As for the snapping of one of the nock’s two shoulders, it is caused by the archer pressing on the nock with his index finger, which fractures that side. This is a serious defect and is most common among beginners to the art of archery.

Its remedy is to avoid (1) pressing the nock with the index finger and to let that finger rest lightly upon the arrow.

Section: The reason the bow quivers with the arrow as it leaves the belly of the bow, and how to correct it (2)

This vibration can arise from fifteen causes (3): four lie in the string, six in the arrow, one in the bow, and four in the archer himself.

The four causes found in the string are: its excessive length, its being too thick, its being too thin, and the disparity that occurs when one of its end loops is wide and the other narrow.

The single cause that lies in the bow is that its two siyahs (outer limbs) are fashioned from different types of wood—one soft, the other hard.

The six causes in the arrow are that its fletching is mismatched: one feather is light and the other two heavy, or vice versa; or one feather lies flat and the other two stand upright, or vice versa; or one feather is broad and the other two narrow, or vice versa; or it may be