Here is another example of a simple error of omission that could have been caught if the student had read the essay aloud or given it to a friend to read. The word "of" should be between "calculation" and "the." That one small error makes the entire sentence awkward and confusing. If the instructor has to reread the sentence to try to understand its meaning, the flow of the essay is interrupted. If this happens often enough in the essay, it gives an overall bad impression on what otherwise might be a very good paper in terms of research.
1 Historical review: Some topics are better understood if a brief historical review of the topic is presented to lead into the discussion of the moment. Such topics might include "a biographical sketch of a war hero," "an upcoming execution of a convicted criminal," or "drugs and the younger generation." Obviously there are many, many more topics that could be introduced by reviewing the history of the topic before the writer gets down to the nitty gritty of his paper. It is important that the historical review be brief so that it does not take over the paper.