On 2007 Jan 21 , at 9:48 AM, [EMAIL PROTECTED] wrote:
I might be mistaken with my views of proper metric usage yet I
fell the need to share the embarrassment of asking if there is a
place held in the proper Si metric system that includes Decimeter.
Tim,
Yes, SI does include the decimetre.
The SI metric system has a basic unit for every type of measurement
and a series of prefixes used to form larger and smaller units. The
officially recognized and sanctioned prefixes DO include "deci-"
which may be appended to any basic unit to form a unit which is one
tenth as big as the basic unit. Thus, for example, it can be used
with "metre" to make "decimetre" where:
one decimetre = one tenth of a metre, or 1 dm = 0.1 m
Of course these relations can be reversed. So, we can write:
one metre = ten decimetres, or 1 m = 10 dm
It is often easier to discuss these things in this second form since
it does not involve fractions.
However, most of the prefixes in the SI metric system are used to
make new units that are 1000 times as big as the next smaller unit,
not just 10 times. To illustrate some of the more common prefixes,
and using "metre" as the base unit for example, we have:
1 gigametre = 1000 megametres
1 megametre = 1000 kilometres
1 kilometre = 1000 metres
1 metre = 1000 millimetres
1 millimetre = 1000 micrometres
1 micrometre = 1000 nanometres
etc.
In the earliest forms of the metric system, there were also prefixes
for every step-of-ten. There were only six at that time. Using
"metre" as the base again:
1 kilometre = 10 hectometres
1 hectometre = 10 decametres
1 decametre = 10 metres
1 metre = 10 decimetres
1 decimetre = 10 centimetres
1 centimetre= 10 millimetres
However, having a new prefix for EVERY factor of ten soon proved to
be too cumbersome. As the metric system was used for larger and
larger things (distances to stars) and smaller and smaller things
(masses of protons and electrons) there would need to be too many
prefixes for convenience. At some point the decision was made that,
when adopting additional new prefixes, only powers of 1000 would be
used.
Since that time, one finds that in most areas, ONLY the powers of
1000 are used. However, hecto-, deca-, deci- and centi- ARE STILL A
PART of SI and there are a number of areas in which some of them are
in quite common use.
The prefix "centi-" is in very prevalently use as the "centimetre",
of course, although there are efforts in some parts of the world
(Australia, for example) to eliminate it and use millimetres instead.
In Europe it is not uncommon to find wine and beer served by the
centilitre or the decilitre.
The land area unit, "hectare", while not itself an SI unit, is
defined as 1 square hectometre and the liquid volume unit,
"litre" (also not an SI unit itself) is defined as 1 cubic decimetre.
There are other examples.
However, generally, there is a tendency to gradually eliminate the
use of the old power-of-ten prefixes in favor of using just power-
of-1000 prefixes. Many people would agree, at least, not to introduce
the power-of-ten prefixes into situations where they are not already
traditionally used. Others would like to see them phased out even in
those traditional uses. While some people vehemently protest any
effort to eliminate those power-of-ten prefixes, others are ardently
in favor of doing just that. Time will tell.
I hope this answers your question and gives you some context for
understanding how the decimetre is (or is not) used.
Bill Hooper
1810 mm tall
Fernandina Beach, Florida, USA
