Grammatically Correct: The writer's essential guide to punctuation ...

GRAMMATICALLY CORRECT
BETTER: The "Save As" feature lets you save an existing file under a new
name (to either the main drive or the extra drive) so that you now have
two copies of the same file.
The next example presents a similar problem:
Error messages are recorded on the local and the host message queues.
The local message queue has the same name as the session. To find out
the cause of the failure, use the information in both message queues.
Readers-even those who understand the jargon-might have
trouble spotting that two of these three sentences are critically
related. The main thread here is that there are two message queues
(whatever those are!) and the user must apply the information in
both queues in order to solve a problem. The secondary information
is that one of these two message queues is identified in a particular
way. Subsuming this secondary information in parentheses would
make the relationship between the first and third sentences clearer.
BETTER: Error messages are recorded on the local and the host message
queues. (The local message queue has the same name as the session.)
To find out the cause of the failure, use the information in both message
queues.
Parentheses can also be employed to make text read more
smoothly and concisely.
A validity coefficient cannot exceed the square root of the reliability
coefficient. For example, if the reliability of a test is. 70, the test validity
cannot exceed .83. If the validity coefficient exceeds the square root of
the reliability coefficient, a sampling error has occurred.
Note the unwieldiness of the third sentence, which repeats the
entire contents of the first. It would be nice to avoid this repetition
by using a pronoun, but the second sentence prevents this, since it
would intervene between the pronoun and its antecedent. (See
"Referring to the Right Antecedent" on page 249.) If this sentence
were enclosed in parentheses, however, the third sentence could
be constructed as though it came immediately after the first. That
is, the second sentence would effectively "not be there" as far as the
rest of the text is concerned. Since it is just an example, subsuming it
does no harm to the flow.
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