十二支
Several coding systems are used to avoid ambiguity. The Heavenly Stems is a decimal system. The Earthly Branches, a duodecimal system, mark dual hours ("shí", or "shíchen" ()) and climatic terms. The 12 characters progress from the first day with the same branch as the month (first "Yín" day () of "Zhēngyuè"; first "Mǎo" day () of "Èryuè"), and count the days of the month.