Cao Rou was a pianist in the prosperous Tang Dynasty. He created subtraction notation for guqin. Later, it was revised and used by Qin people in previous dynasties.
His greatest contribution to Qin culture is that he created the guqin minus sign on the basis of previous works on Qin studies. Although the spectral subtraction was basically perfect in the Ming Dynasty, it did not leave the basis of Cao Rou's spectral subtraction.
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The spectral words of subtraction spectrum are mostly composed of right-handed fingering, left-handed fingering and general terms. There are eight basic fingering methods for the right hand, commonly known as "four fingers and eight fingers", that is, the corpse (split) palm (support) of the thumb, the wooden palm (wipe) palm (pick) of the index finger, the hook (hook) hook (easy) of the middle finger and the ding palm of the ring finger. Other fingering methods are actually composed of eight variations.
Fingering with the left hand mainly includes: one (Yin), one (Yan), no (poke), lift (note), up, down, clip (Jin Fu), root (hot compress) and lattice (one).
Since ancient times, there have been a lot of literatures about subtractive chromatography. His important figures can be found in Legacy of Ancient Times, Complete Works of Qin Shu and a large number of Ming and Qing music scores. Nearby works include Cha Fuxi's Notes on Guqin Fingering and Guan Pinghu's Study on Guqin Fingering, which can be used for reference.