The Proofreading service Is an essential part of the Quality Control System. 

It looks for consistency (style guides and checklists) and uniformity (in-house rules and procedures) to eliminate discrepancies, wrong interpretation of terms and language idioms and inaccuracies on the final result.

Linguistic Proofreading deals with intrinsic properties of the language itself (grammatical mistakes, misspellings, mistyping, incorrect punctuation...)

Technical Proofreading as to do with the application of language to describe a technical or scientific subject or discipline, thus concentrates the attention on the rules and fundamentals of that discipline.