A critical apparatus (jiaokanji 校勘記, literally "records of comparing editions") serves to compare various editions of individual texts and to show up differences in words, sentences and the structure of the text.
The earliest regular critical apparatus is Lu Deming's 陸德明 Jingdian shiwen 經典釋文 from the Tang period 唐 (618-907), a critical edition of and commentary to the Confucian Classics and the books Laozi 老子 and Zhuangzi 莊子.
The most important apparati critici from the Song period 宋 (960-1279) are Zhang Chun's 張淳 Yili shiwu 儀禮識誤 (to the Classic Yili 儀禮), Fang Songqing's 方崧卿 Hanji juzheng 韓集舉正 (to the collected writings of Han Yu 韓愈), Peng Shuxia's 彭叔夏 Wenyuan yinghua bianzheng 文苑英華辯證 (to the anthology Wenyuan yinghua 文苑英華) and Yue Ke's 岳珂 Xiangtai shushu kanzheng Jiujing sanzhuan yange li 相臺書塾刊正九經三傳沿革例 (see Xiangtai wujing 相臺五經).
During the Qing period 清 (1644-1911) the critical school made great progresses in the analysis of ancient writings and produced a large number of critical apparatuses, not only to the Classics and related texts, but to all types of writings on philosophy, history, geography or poetry. Some of these apparatuses were published together with the transmitted text, but there were also some separate editions. The most important results in the field of Confucian Classics are Ruan Yuan's 阮元 Shisanjing zhushu jiaokanji 十三經注疏校勘記 and Lu Wenchao's 盧文弨 Qunshu shibu 群書拾補.
In the 1960s and 1970s the Zhonghua shuju press 中華書局 published critical editions of the twenty-five official dynastic histories that are today used as the standard editions.
A critical apparatus notes down the following characteristics: Differences in wording (like yi ben zuo mou 一本作某 "one edition writes xyz" or mou ben zuo mou 某本作某 "this and that edition writes xyz"), additional words (like mou ben mou xia you mou zi 某本某下有某字 "this and that edition adds the word(s) xzy after the words abc"), missing words (like mou ben wu mou zi 某本無某字 "this and that edition omits the word(s) xyz"), superfluous words (like mou ben mou zi yan 某本某字衍 "this and that edition adds in excess the word(s) xyz"), different order of words (like mou ben mou mou er zi hu yi 某本某某二字互乙 "this and that edition changes the words xyz (without leading to a senseless text)", or mou mou er zi yan, dang cong mou ben zuo mou mou 某某二字衍，當從某本作某某 "adds excess words; should be read like in this and that edition as xyz"), correction of errors (like mou dang zuo mou 某當作某 "xzy should be abc"; or mou yi dang zuo mou 某疑當作某 "xyz might be read as abc"), or the order of sentences (like mou ben mou ju zai mou ju xia 某本某句在某句下 "this and that edition writes the sentence or phrase xyz after the sentence or phrase abc").