What does the cryptic crossword clue "Chapter I revised to show a type of graph (3,5)" mean?

The definition is "graph". The wordplay uses an anagram. anagram of CHAPTER + I = PIECHART; definition: "graph" The answer is PIECHART.

Chapter I revised to show a type of graph (3,5)

Daily Mail Cryptic #17043 | 20 Across | 2023-02-28 flower