SOME archers, for instance the Egyptians, have favored the use of a thin and hard string, maintaining that it is better suited for casting the arrow, less visible on the bow, and more telling against the enemy. They were guided in their choice by the fact that the strings used in competitive archery [flight-shooting] are always thin, with all archers agreeing on this specification.
Others (namely, all the Persians) have preferred thick and coarse strings, asserting that they are better in every way. Ṭāhir al-Balkhi once said that he had examined a bow belonging to a certain Persian against the arrow of which none could protect himself because of its force and penetration, and found out that the bow was as flexible as those in current use, but that its string was coarse and as thick as a finger and that the metal head of its arrow was very large. He, therefore, made himself one exactly like it and tested it; only to find it very good. A certain archer stated that the coarse string is better for the bow: more penetrating, more easily drawn, and superior to the thin in warfare and target shooting; while the thin string is better for competitive shooting and for shooting at distant marks. Ṭāhir declared that the thick string is more deadly at short distances and the thin is more telling at long distances.
The thinness and thickness of the string, as well as its relatively appropriate size, are determined by bracing its bow, drawing the string with the thumb and index finger the length of one and a half spans, quickly releasing it and listening to its twang. If the twang is sharp and high, the string is too thin for the bow; if it is moderate in sharpness and lowness, the string is just right; if it is low, the string is too thick.