Qinzhi 琴旨 "Compass to the zither" is a book on the small zither (qin 琴) written during the Qing period 清 (1644-1911) by Wang Tan 王坦 (mid-18th cent.), courtesy name Jitu 吉途, who came from Nantong 南通, Jiangsu.
His 2-juan long book is based on the official compilation Lülü zhengyi 律呂正義 (part of the collection Lüli yuanyuan 律曆淵源), but goes more into detail when explaining the application of the five tones (wusheng 五聲) to the zither. The physical relation of the five tones to each other is very important for the tuning of the strings of the zither, he says, and has therefore to be investigated in a very exact manner.
It is not possible to make use of the system of the twelve pitch pipes (lülü 律呂) that are based on the length, diameter and circumference of twelve pipes whose dimensions are derived from the basic Yellow Bell pipe (huangzhong 黃鐘). In this system, the Zhonglü pipe 仲呂 corresponds to the tone jiao 角, a method not applicable for the zither. Wang Tan also explains how the tone zhi 徵 can be found on the third and the fifth string of the zither, and which effects a change of the mode has for the position of tones.