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 high tone, and ˧˥˩ means one that begins mid-low, then goes high and ends low.
Tone letter on Wikipedia.Wikipedia 