I charge a different rate for each of the three levels of editing: developmental, copy, and proofreading. Developmental editing refers to major editing at the page and chapter level. Copy editing happens in paragraphs and sentences, addressing some organizational concerns and any content edits that are required. Proofreading is a final coat of polish, exclusively dealing with grammatical and mechanical errors (a dropped "s," a misspelled word, incorrect quotation marks, citations, etc).