The definition of a proofreader, according to The Society for Editors and Proofreaders:

After material has been copy-edited, the publisher sends it to a designer or typesetter. Their work is then displayed or printed, and that is the proof – proof that it is ready for publication. Proofreading is the quality check and tidy-up. 

Page proofs or draft web pages are usually the last chance to see everything – words, footnotes, images, graphs, tables – integrated with the design before going public. Now the work is largely fixed and changes have to be limited.

The proofreader uses care, judgement, skill, knowledge and experience in checking that the work of author, editor and designer/typesetter is satisfactory, marking amendments and advising the client of problems, all with the aim of optimising the result while minimising cost of production and delay to publication.

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