• 3 underlying tones: /H/, /L/, /F/ (unitary), and possibly /HL/ (sequence)
  Schuh's arguments for treating /F/ and /HL/ as underlyingly different tones are: (a) they have different distributional restrictions; (b) they have different alternation behaviors; and (c) they may have different historical origins.
  (a) /F/ is restricted to monosyllabic suffixes/clitics (all examples Schuh lists have long vowels) or light (CV) finals of disyllabic substantives provided the preceding syllable is heavy (CVV or CVC) and High-toned. /HL/ occurs on heavy monosyllables or heavy finals of di- and polysyllabic words with Low tone(s) preceding it. One example in which /HL/ occurs in a word-medial heavy syllable is also found.
  (b) /F/ -> Falling after High before pause; /F/ -> H elsewhere, i.e., after L before pause and in any phrase-medial environment. /HL/ does not alternate.
  (c) Most /HL/ came from borrowings from Hausa, Arabic, Kanuri, etc.
  
  Synchronically, a more likely account might be: there is only one underlying contour tone /F/ (/HL/), which can occur on heavy syllables and word-final light syllables. When a F-carrying light syllable is not in final position anymore due to suffixation, F -> H. A preceding Low tone also wipes out the High target in the Fall.
• 3 surface tones: [H], [L], [HL]
• Tone bearing unit: Possibly syllable. Vowel length is contrastive in nonfinal syllables. Schuh considers vowel length to be allophonic in word-final syllable for non-verb substantive items: monosyllables all end in long vowels, all other words end in short vowels. The long vowels that carry Schuh's /HL/ in final syllable of longer words are considered exceptional by Schuh. See discussion in "Underlying Tones."

Contour Simplification:

Tone Raising/Lowering: