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

STYLE
with a consonant sound, precede it with a, even if the first letter is
a vowel.
an RCM P officer
an NBC program
a UV light
a RAM capacity
a NATO meeting
an URN publication
• Occasionally, a single word is abbreviated to two capital letters
(more typically, abbreviations of single words appear in lowercase).
Be certain in such cases that you capitalize both letters.
Each user must have a valid ID number in order to access the system.
[not ld]
If that's what you want, it's OK with me.
[not Ok]
Anything good on TV tonight?
[not Tv]
• If an all-caps abbreviation is pluralized, be sure that the pluralizing
s appears in lowercase. If you put it in uppercase, it could look
like part of the abbreviation itself.
Guests are asked to return their RSVPs as soon as possible.
[not RSVPS]
The RNs' shifts were posted by the front desk.
[not RNS']
For more on all-caps abbreviations, see the discussions under
"Period" on page 109 and "Apostrophe" on page 198.
HEADINGS
• Nonfiction writing, if it is of any significant length, generally
calls for headings of different levels: high-level headings to introduce
main sections, lower-level headings to introduce subdivisions of a
main section, still lower-level headings to introduce subdivisions of
a subdivision and so on. It is very important that headings of the
same level always appear the same way and that those of different
levels be visually distinct. The typography of a heading serves as a
visual cue to readers, informing them whether what follows is a
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