In the illustrations of the IPA Handbook, this letter may come before a word or syllable to indicate prosodic pitch, and after a word or syllable to indicate lexical tone.
When this letter occurs in ligature with other tone letters, they together indicate the pitch contour of the tone. For example, ˨ means a level mid-low tone, and ˨˩˧ means one that begins mid-low, then drops to low and ends mid.
Tone letter on Wikipedia.Wikipedia 