Explanation
PerfectIt suggests there may be a possible issue if an abbreviation is defined twice or more.
Suggestion
Defining an abbreviation more than once can make a document seem cluttered and confusing. In most instances, the phrase should be spelled out once when the abbreviation is introduced and not spelled out after that point.
Not all abbreviations need to be defined. However, if authors choose to define an abbreviation, it should be introduced at the first instance with either the abbreviation or definition in parentheses.
For example:
The tallest buildings are in the CBD (Central Business District).
The tallest buildings are in the Central Business District (CBD).
Exception
Authors may wish to define an abbreviation more than once if readers of technical publications are likely to skip chapters/sections and require clarification at the start of each.
However, in these cases a table of abbreviations is usually preferred. Use PerfectIt’s Table of Abbreviations feature (available via the Reports menu) to automatically generate a list that can be copied and pasted into a document.