The following reference is from "Getting Your English Right, Tapir, Trondheim 2001"

Marking titles, abbreviations and acronyms

Do NOT use full stops: after titles, headings and sub-headings;

after units:
WRITE: cm, in, kg, Hz,
NOT: cm., in., kg., Hz.

within capitalized abbreviations or acronyms:
WRITE: VDU, USA, NATO
NOT: V.D.U. U.S.A. N.A.T.O.

Use full stops between letters if you form and use lower-case abbreviations:... the e.s.r. spectrum (electron-spin-resonance spectrum)
In general, however, lower-case abbreviations are not used in scientific and technical writing.

Use full stops after abbreviations formed by cutting off the end of a word, such as:
No. Nos. Fig. Figs. Sun.

In correspondence, a useful rule is to use a full stop after an abbreviation of a personal title, except (in BE) when the abbreviation contains the first and last letters of the abbreviated word, examples:

Dr, Mr, Mrs, Co., Ltd.
NOT: Dear Mr. Jones (in BE)

If this source is to be believed this is a genuine difference between US and British English.

I would also mention that some sources suggest that the use of full stops (periods) in abbreviations is becoming less common in both forms of English.

Richard English

[This message was edited by Richard English on Wed Dec 24th, 2003 at 12:41.]

Wow, some of those are news to me. For example, I have always used periods with inches in order not to confusing it with the word "in." While you see USA a lot (as in the newspaper USA Today), you also see U.S.A. I thought I had a source at home, but I don't.

To be honest, I don't think we in the U.S. (no periods? If not, what about "us?") are as consistent as we could be. I do use periods after Mr., Mrs., Dr., but not Kg or mL or gm, or cm, but I do with inches because of "in." Then again, maybe I'm not consistent, but the others in the U.S. are.

After discussing the use of periods with abbreviations here, and seeing differences between our U.K. and our U.S. writers, I am terribly confused! When, in U.S. writing, do I use periods?

For example, in today's newspaper they used U.S. and UN in the same sentence. Why does U.S. have the periods and UN doesn't? Is there a rule that I can use with consistency?

Is it just me or does the imprint 'Tapir, Trondheim' not inspire sober confidence?

Various issues here. Metric units have symbols, not abbreviations, and '10 kg' is the only correct form, no punctuation and no plural.

The distinction between contractions ('Dr' containing the last letter) and abbreviations ('Capt.' cut off before the end) started to be used consistently by British printers from about 1900. It hasn't necessarily percolated completely into common use.

These days journals and even books often have quite slapdash approaches to punctuation, and some go the whole hog and write 'eg' and 'ie'.

I suspect that the writer was trying to ensure that there was no confusion between the pronoun US and the abbreviation for United States.

However, I suspect that any such confusion is unlikely in most normal passages; only if the whole passage were to be in upper case would there usually be any possibility of confusion.

So the headline "HELP US - BUSH PLEA" would need additional punctuation if its true meaning is to be understood at first glance. Few other passages would need such extra aid.

Richard English

I leave them all out when word-processing: Dr, Co, Ltd, ie, eg, etc. None of them would be misunderstood.

quote:

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when the abbreviation contains the first and last letters of the abbreviated word, examples:

Dr, Mr, Mrs, Co., Ltd.

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Which reminds me of something my students asked me the other day... I always thought Mrs. (with or without a fullstop/period) was an abbreviation of 'Missus'. Or is that the written out pronunciation of the abbreviation? If so, what word does Mrs. abbreviate?

Silly me. I just opened the OED to check and found the answer. But I'll post this anyway in case anyone else wondered. Mrs. is the abbreviation of Mistress which was corrupted into Missis or Missus.