The scholars of Qing Dynasty, among whom Duan Yucai was, were puzzled by the problem of tone value because of their sight being confined to the Mandarin in North of China.

• 段玉裁等乾嘉大师在北系官话的背景下研究上古音,研究目光受到了局限,只有大类之别而为音值的探求所困扰。