Punctuation: Period
From Manual of Style by University of Chicago Press:
A period is used to indicate the end of a complete sentence.
I. Put a period after most abbreviations.
Macmillan & Co., Mr. Smith, St. Paul, No. 1, Chas., ibid.
A. Treat the metric symbols as abbreviations:
10 mm.
B. Exceptions:
1. Do not use periods with the chemical symbols, nor the phrase “per cent.”
O, Fe; 2 per cent
2. Do not use a period, in technical matter, after the recognized abbreviations for epochs:
AD (Anno Domini)
BC (Before Christ)
CE (Common Era)
BCE (Before Common Era)
IE (Indo-European)
OE (Old English)
II. Use no period after Roman numerals.
Vol. IV
A. This is true even when Roman numerals have the value of ordinals:
Louis XVI was on the throne.
B. Exception:
Roman numerals used in an outline are followed by a period.
III. When using quotation marks, the period is placed inside.
Please read Tennyson’s “In Memoriam.”Sylvie said, “It’s raining.”
IV. When using parentheses, the period is placed according to use.
A. Place the period inside the parentheses
when the matter enclosed is an independent sentence and forms no part of the preceding sentence:
John dropped the hammer on his toe. (It hurt badly.)
B. Place the period outside the parentheses
when the matter enclosed is an independent sentence is part of the preceding sentence.
Fried sweets are tempting (for instance, doughnuts).
