The tones of ancient Chinese can be divided into four tones: flat, up (sh m 4 ng), falling tone and entering tone. "Ping" refers to the flat tone among the four tones, including Yin Ping and Yang Ping. "Xu" means

Among the four tones, there are three tones: up, down and middle.

Modern Chinese pronunciation can simply classify one or two sounds as flat and three or four sounds as flat, but when writing metrical poems, it should be pronounced according to ancient sounds. For example, the word "Pai" in this poem is flat in modern pronunciation, but flat in ancient pronunciation.

Now you can refer to Pingyunshui or China's new rhyme when you write poetry. Pingyunshui is classified according to ancient pronunciation, while Chinese new rhyme is classified according to modern pronunciation.