[2] In its initial form, Bamum script was a pictographic mnemonic aid (proto-writing) of 500 to 600 characters.

The fourth system, called Rii Nyi Nsha Mfw' after its first four characters, was developed around 1907–1908.

These first five systems are closely related: All were progressively simplified pictographic protowriting with logographic elements.

This phase marks a shift to a full syllabic writing system able to distinguish 160 syllables.

Adding the inherent vowel of the syllable voices a consonant: tu + u = /du/, fu + u = /vu/, ju + u = /ʒu/, ja + a = /ʒa/, ʃi + i = /ʒi/, puə + u = /bu/.

The two diacritics are a circumflex (ko'ndon) that may be added to any of the 80 glyphs, and a macron (tukwentis) that is restricted to a dozen.

The circumflex generally has the effect of adding a glottal stop to the syllable, for instance kâ is read /kaʔ/, though the vowel is shortened and any final consonant is dropped in the process, as in pûə /puʔ/ and kɛ̂t /kɛʔ/.

Sometimes, however, the circumflex nasalizes the vowel: nî /nɛn/, pî /pin/, rê /rɛn/, jûʔ /jun/, mɔ̂ /mɔn/, ɲʒûə /jun/ (loss of NC as with glottal stop).

Others are idiosyncratic: ɲʒə̂m /jəm/ (simple loss of NC), tə̂ /tɔʔ/ (vowel change), ɲî /ɲe/, riê /z/, m̂ /n/, ʃɯ̂x /jɯx/, nûə /ŋuə/, kɯ̂x /ɣɯ/, rə̂ /rɔ/, ŋkwə̂n /ŋuət/, fɔ̂m /mvɔp/, mbɛ̂n /pɛn/, tî /tɯ/, kpâ /ŋma/, vŷ /fy/, ɣɔ̂m /ŋɡɔm/.

In order to do this, the Project examined hundreds of important documents transcribed in the current and most widely employed variant of the Bamum script: A-ka-u-ku (after its first four characters).

The goal of the project team was to identify the most prominent forms of the various Bamum characters, as there have been many different styles employed by literates over the years.

In particular, the Project examined documents in the script known to have been written by the three most famous Bamum script literates: King Njoya and his colleagues, Nji Mama and Njoya Ibrahimou (younger brother of Nji Mama, also a well known Bamum artist).