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 low tone, and ˩˧˩ means one that begins low, rises to mid and ends low.
Tone letter on Wikipedia.Wikipedia 