He consulted with William A. Smalley, a missionary studying the Khmu language in Luang Prabang Province at the time.
Concurrently, Yves Bertrais, a Roman Catholic missionary in Kiu Katiam, Luang Prabang, was undertaking a similar project with Chong Yeng Yang and Chue Her Thao.
The two working groups met in 1952 and reconciled any differences by 1953 to produce a version of the script.
RPA indicates tone by letters written at the end of a syllable,[4] similarly to Gwoyeu Romatzyh or Zhuang, rather than with diacritics like those used in the Vietnamese alphabet or Pinyin.
Unlike Vietnamese and Chinese, all Hmong syllables end in a vowel, which means that using consonant letters to indicate tone will be neither confusing nor ambiguous.