Post by John WoodgateNo, the unit is Volt, named after mr Volta. so, it's 6,3 Volt or 6,3 V,
never volt, volts or Volts
The symbol is V, but the unit name is NOT capitalized. See IEC 60027 or
ISO 7000.
The answer is that in formal scientific work they should not, so '6.3 volt',
but in text for the general public that is unfamiliar, and pluralization
is preferable.
This seems to touch two different conventions, at least according to the
National Physics Laboratory (UK) and to the National Institute of
Standards (US). The first convention is that unit *names* are
pluralised, as opposed to unit *symbols*, which are not pluralised. For
example: 6 volts (not 6 volt); 6 V (not 6 Vs). That first convention is
valid for formal scientific works as well as for texts for the general
public. The distinction between the two types of texts arises in
connection with a second convention, which says that for the key
elements of a scientific paper the use of unit symbols should be
preferred to the use of unit names. But when someone does use the unit
names, they are pluralised.
To quote from the recommendations of the NPL:
"If the spelled-out name of a unit is used, the normal rules of English
are applied."
"For unit values more than 1 or less than -1 the plural of the unit is
used and a singular unit is used for values between 1 and -1."
To quote from the _Guide for the Use of the International System of
Units (SI)_, on the NIST website:
"Plural unit names are used when they are required by the rules of
English grammar. They are normally formed regularly, for example,
"henries" is the plural of henry."
http://physics.nist.gov/Pubs/SP811/sec09.html
"This Guide takes the position that the key elements of a scientific or
technical paper, particularly the results of measurements and the values
of quantities that influence the measurements, should be presented in a
way that is as independent of language as possible. This will allow the
paper to be understood by as broad an audience as possible, including
readers with limited knowledge of English. Thus, to promote the
comprehension of quantitative information in general and its broad
understandability in particular, values of quantities should be
expressed in acceptable units using the Arabic symbols for numbers,
that is, the Arabic numerals, not the spelled-out names of the Arabic
numerals; and the symbols for the units, not the spelled-out names of
the units. (...) Occasionally, a value is used in a descriptive or
literary manner and it is fitting to use the spelled-out name of the
unit rather than its symbol. Thus this Guide considers acceptable
statements such as "the reading lamp was designed to take two 60-watt
light bulbs," or "the rocket journeyed uneventfully across 380 000
kilometers of space," or "they bought a roll of 35-millimeter film for
their camera." "
http://physics.nist.gov/Pubs/SP811/sec07.html#7.6
(Of course, in the last sentence quoted above, the qualifiers "60-watt"
and "35-millimeter" are in the singular not because of the rule about
the pluralisation of unit names used as nouns, but only because they
are used to qualify "light bulb" and "film".)
--
Jean