Gwoyeu Romatzyh
Like Chao's other invention, Gwoyeu Romatzyh, romanized General Chinese uses tone spelling. However, the system is somewhat different. The difference between the "yin" and "yang" tones is indicated by the voicing of the initial consonant, which is possible because the original voicing distinctions are retained. Given that some tones are indicated by changing rather than adding letters, writing tone requires on average only one additional letter for every three syllables of text.