"華" (Hoa) has been omitted due to naming taboo), it can be guessed that this text was written during the reign of Emperor Thieu Tri (Emperor Thiệu Trị's mother's name was "Hồ Thị Hoa" 胡氏華). At the end of the text's preface, there is a line "五星聚斗南城居士阮子書" (Ngũ Tinh Tụ Đẩu Nam Thành Cư Sĩ Nguyễn Tử Thư). Through this inscription, it can be known that the author of Quoc Am Tan Tu is a layman with the surname Nguyen (阮) in Nam Dinh citadel (南定) with the nickname Ngu Tinh Tu Dau (五星聚斗). Quoc Am Tan Tu is a type of phonetic script made from the strokes of Chinese characters and Nom characters (similar to Hiragana and Katakana of Japanese or Chinese Zhuyin). Based on the pronunciation of Vietnamese, there are 22 "cán tự" 幹字 and 110 "chi tự" 枝字 ("cán" means trunk, "chi" means branches, "tự" means character). The cán tự is used to record the first consonant, and the chi tự is used to write the rhyme. Each character is named with a word that rhymes "ông" with the first consonant being the first consonant that the character signifies, for example, the word "đ" denotes the consonant "đ" is named "đông" ( similar to today, the Vietnamese call the consonant "đ" the sound "đờ"). Quoc Am Tan Tu does not distinguish between "d" and "gi" as in Quoc Ngu (possibly because the author followed the Northern accent when "d" and "gi" sound almost the same). There is a shank used to record the initial consonant /ʔ/, which is named "ông". The author of Quoc Am Tan Tu used four stroke types: (一), (丨), (丶), (丿) (also including "㇏" as a variant of "丶") to create the characters. Every character (including all "trunk" and "branch" characters) has a total of four strokes. Most of the characters only use two or three stroke types, but the total number of strokes is exactly four. Quoc Am Tan Tu uses the traditional "tone" division, the tones are divided into four categories: "bình" 平, "thượng" 上, "khứ" 去, "nhập" 入. Each type is further divided into two degrees "yin" 陰 and "yang" 陽. There are eight tones in total: Âm bình or yin ping 陰平: is the "thanh ngang" as it is called today. Dương Bình or yang ping 陽平: is Thanh Huyền as it is called today. âm thượng or yin