A “the” is missing before “unit portion.”

Existing Wording:

The number portion of a quantity can be an integer or decimal, and unit portion is a (single-quoted) string representing a valid Unified Code for Units of Measure (UCUM) unit or calendar duration keyword, singular or plural. To avoid the possibility of ambiguity, UCUM codes shall be specified using the case-sensitive (c/s) form.

Proposed Wording:

The number portion of a quantity can be an Integer or Decimal, and the unit portion is a (single-quoted) String representing a valid Unified Code for Units of Measure (UCUM) unit or calendar duration keyword, singular or plural. To avoid the possibility of ambiguity, UCUM codes shall be specified using the case-sensitive (c/s) form.