Why there is no "4" and "7" notes in the key of Guzheng?

The reason why there are no "4" and "7" notes in the key of guzheng is that traditional Chinese music is based on the pentatonic scale, and there are only five positive tones, 1, 2, 3, 5 and 6, and all other tones including 4 and 7 belong to partial tones, which are usually not set when the guqin, guzheng and other instruments are tuned. All other tones, including 4 and 7, are partials, and are not usually set during stringing of guqin and guzheng instruments. However, these tones can be obtained through the technique of "Pressing Tones", and the actual performance of these tones depends on the repertoire and the tuning of the instrument.