Pinyin, also known as the Chinese Phonetic Alphabet, is the official phonetic alphabet for denoting Chinese characters with the Roman alphabet. It was created by a committee of prominent Chinese linguists and other scholars in 1955, and promulgated in February 1958 after being approved by the National People's Congress of the PRC. A syllable in  Putonghua  (Standard Chinese) may include a  shengmu  (initial), a  yunmu  (final), and a  shengdiao  (tone). The initial is the consonant at the head of the syllable. For example, the initial for "ma" is "m." If the syllable starts with a vowel (such as "an" or "ou"), it can be considered a "zero-initial" syllable. The final follows the initial in the syllable. It consists of at least one vowel and sometimes one or two consonants. The pinyin system has 21 initials and 35 finals (including 6 single-vowel finals, 13 compound-vowel finals, and 16 nasal finals). The tone is the pitch of the syllable. In Chinese, there are four tones denoted with diacritics:  yinping  (high and level, ˉ),  yangping  (rising, ˊ),  shangsheng  (falling-rising, ˇ), and  qusheng  (falling, ˋ). The diacritic is placed above the letter that represents the syllable nucleus. For example, the syllable "chàng" includes an initial ("ch") and a final ("ang"). Since "a" represents the syllable nucleus, the tone "ˋ" is placed above it. Syllables with the same initial and final but different tones denote different characters. For example, the syllables "dā," "dá," "dǎ," and "dà" may respectively denote 搭 (put up), 达 (arrive), 打 (hit), and 大 (big).