It was originally used by government officials equal or superior to Sakan to submit a report personally to their superiors, and it was created in a format in which a Chinese character "cho" (牒) was written at the beginning, the main text was concluded with a phrase "tsutsushimite chosu," (謹牒) the date and Isho (rank and name in a row) were written in the last line and a character "cho" (牒) was inserted below Isho. It is believed that cho, as referred to in Kushiki-ryo (law on state documentary forms in the Yoro Code) of Taiho Ritsuryo (Taiho Code) (Ritsuryo law), refers only to such documents. Furthermore, after Ryoge no kan (a post outside the original Ritsuryo code created by Imperial edicts) was established, cho was generally used for official documents in relation to Ryoge no kan (cases in which the sender or the receiver, or both, were Ryoge no kan) because in some cases no hierarchical relationship existed among Ryoge no kan.
In 719, however, as to exchanges of documents between Sogo (a monk of a managerial post)/Sango (three monastic positions with management roles at a temple) and Zokkan government officials, having used cho because fundamentally no hierarchical relationship existed between them, it was stipulated that a form of "i" (移) should be used by replacing Chinese characters "i" (移) with "cho." Such stipulation was reflected in Kushiki-ryo in the Yoro Code which was being compiled those days, and added as another form of cho. Cho sent by Daijokan (Grand Council of State) or In no cho (Retired Emperor's Office) to Sogo, etc. was especially called daijokancho or innochocho respectively. In the mid Heian period, daiokancho and innochocho were replaced by Kan senji (an edict from Daijokan [Grand Council of State] which had the status of a binding official document) and Inzen (a decree from the retired Emperor) which did not require shoin (a ceremony to seal documents issued by the government) while the number of cho issued increased due to an increase in number of Ryoge no kan in agencies such as Kurodo dokoro (the Office of Imperial Household Logistics) and Kebiishicho (Office of Police and Judicial Chief). Especially Kurodo dokoro, which governed important affairs of the state, issued many cho, and more and more official documents which should have been issued in other forms such as i, zi or fu were issued as cho. That is why cho started to be used for letters of escalation from individuals and orders to individuals, which should have been issued in a form of zi.