NIST treats them as symbols, Bill. Some of them, such as lb and oz, are
not abbreviations, except in languages other than English. See NIST SP
811, for instance.
Some are accepted for use with the SI and thus their symbols should
never be followed by a period, except when they end a sentence. Examples
are h and min. You may see this in the Brochure.
You are correct, as far as I know, in saying that there is no official
standard for U.S. Customary units and their symbols. After all, they do
not form a system and are not organized and related beyond the basics in
any document. Instead, they rely on tradition for names and on SI units
for extent. This leads to some interesting problems. The teaspoon (tsp)
traditionally is 1/6 of a fluid ounce but the FDA defines it as 5 mL,
and the USDA matches that.
Jim
Bill Hooper wrote:
On Aug 7 , at 10:11 AM, James Frysinger wrote:
This is outside the metric system, but there is no need for a
period following the symbol "oz" since it is a symbol and not an
abbreviation.
I'm not sure that is right, Jim.
In SI the short forms are officially called symbols but I think the
short forms for older, non-metric units have always been identified as
abbreviations. Thus, the abbreviation for fluid ounce may be written as
"FL. OZ." or "fl. oz." or "Fl. Oz." etc. (and even with script letters).
This is not typically done with a symbol. A symbol (like $ or # or @) is
always the same. Thus, SI short forms, since they are always the same
(never M for metre or mw for megawatts), are symbols, not abbreviations.
We can cite official BIPM documents to verify that the SI short forms
are called symbols. I know of no such documents that might classify
other, non-SI short forms as symbols.
Since "oz." and "fl. oz." etc. are abbreviations, they would ordinarily
be followed by a period. In passing, however, I note that some modern
styles tend to omit the periods at the end of abbreviations. As usual,
abbreviations have such variations in form while symbols usually do not.
Regards,
Bill Hooper
Fernandina Beach, Florida, USA
==========================
Make It Simple; Make It Metric!
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James R. Frysinger
632 Stony Point Mountain Road
Doyle, TN 38559-3030
(H) 931.657.3107
(C) 931.212.0267
