Why is proofreading required after editing?

Many students consider editing as the final step of revising and assessing any academic document. While substantive editing is comprehensive and covers quite a lot of aspects while checking the documents, it is not the ultimate check. Proofreading is the next step, which can be thought of as the culmination of revision for an academic document. A proofreader goes through the minute aspects and checks the presentation of the document, be it a thesis, dissertation or an essay. Here is a comparison which will clarify the difference between editing and proofreading:

So we see that while editing is mainly concerned with the quality and accuracy of all the chapters or sections of an academic work, proofreading concentrates upon the presentation issues. Proofreaders make sure that there is not a single spelling mistake or typo error. They even check the punctuations and spacing closely and mark all the errors.

Proofreaders use a set of symbols called proofreaders marks, which are easy to understand and denote certain errors. These are for editors and other proofreaders, who recheck the work, as well as for writers, who make corrections. Here is a list of symbols that are commonly used.