Gustaf has raised an important question. When the English-speaking countries
decided to metricate, why did they generally suppress the prefixes hecto,
deka, deci, and centi? Can anyone give us a documented historical answer? In
the United States, for example, multiples like hectogram, deciliter, and
centiliter are not legal for retail trade. The centimeter is legal, but most
products are labeled in millimeters instead. The prefix deci is legal only
in square decimeter (rarely used). Let me summarize this whole prefixes
issue, which seems to elicit such strong emotions:
FIRST ARGUMENT
These prefixes (not powers of 1000) are clearly simpler for everyday
lengths, masses, areas, and volumes--especially when people are not doing
technical calculations. In ordinary life, people very rarely measure things
to the millimeter, and they NEVER measure to the gram or milliliter. Nothing
is packaged to gram or milliliter precision, and household measuring devices
aren't that accurate. Even a laboratory graduated cylinder can't measure a
liter to 1 mL precision. Mandating only g, mL, and mm means that folks must
deal with useless zeroes and ridiculously false-precise numbers. Unnecessary
digits and false precision are the bane of our existence--by far the biggest
complaint of ordinary folks who otherwise support metrication. In the 1999
survey by the UK National Federation of Consumer Groups, 67% supported
metrication, but 90% OPPOSED prefixes that weren't "user friendly." A
typical respondent's comment was, "I was brought up on the Continent and
looked forward to the conversion, but that stupid insistence on millimetres
put me right off!"
OPPOSING ARGUMENT
These prefixes are "irregular" and violate the normal pattern. They are
little used in science and technology, or in everyday life for quantities
other than length, mass, volume, and area. In science and technology, they
are NOT convenient and make calculations more complicated. Science and
technology deal with a wide range of values requiring many prefixes, and
the "irregular" prefixes add needless complexity without any advantage.
Values are precise, not rounded nominal sizes, so "useless zeroes" are not a
concern. Even for rounded product sizes, there is usually no advantage. For
example, 60 W or "sixty watts" [3 syllables] is easier than 6 daW or "six
dekawatts" [4 syllables]. Most importantly, a calculator (set to ENG
display) automatically gives answers in powers of 1000, but it cannot be set
to automatically give answers in powers of 10^-1, 10^2, 10^1, or 10^2. So
recording an answer with an "irregular" prefix requires bothersome manual
manipulation of the decimal point and the possibility of a mistake. This is
especially true for volume units like centiliter and deciliter that are not
coherent. When you calculate the volume of an object from its dimensions,
you get an answer in cubic meters or one of its multiples. It is hard enough
to remember that the prefix must be cubed along with the unit and that
several multiples have old-metric "nicknames" (liter, milliliter, and
microliter). But at least you don't have to move the decimal point. What you
see is what you get:
E-3 m3 = dm3 = L
E-6 m3 = cm3 = mL
E-9 m3 = mm3 = �L
But deciliter, centiliter, and hectoliter aren't ANYTHING cubed. You have to
move the decimal point.
dL = 100 cm3 = 100 mL
cL = 10 cm3 = 10 mL
hL = 0.1 m3 = 100 L
PRACTICES THAT VIOLATE BOTH ARGUMENTS
Curiously, Europeans don't seem to use the convenient prefixes for large
quantities. My otherwise very bright and capable European students
(including many from Sweden and Germany) will write long rows of useless
zeroes instead of a simple hm3, Mg, or Tg. (To our European friends: is this
typical of everyone?)
No one seems to use dekagram, even though it would be convenient for the
range of small masses encountered in everyday life. No doubt that's because
it's harder to both write and say than grams: 2 dag or "two dekagrams" [4
syllables] is more work than 20 g or "twenty grams" [3 syllables].
The hectometer (hm) would be convenient for flight altitudes, if aviation
ever metricates.
The irregular prefixes are used in science and technology as a subterfuge to
avoid giving up obsolete, non-SI, non-coherent metric units:
(1) dekanewton (daN) is sometimes used for forces because it is close to the
obsolete kilogramforce (kgf) or kilopond (kp), even though most values could
be more easily expressed in kilonewtons (kN). This practice seems to be
declining.
(2) dekapascal (daPa) is used by audiologists because it is close to the
obsolete mmH2O they formerly used, even though the values involved could be
more simply expressed in kilopascals (kPa). This practice has recently
become firmly entrenched.
(3) hectopascal (hPa) is used for atmospheric pressure because it is the
same as the obsolete millibar (mb), even though the values could be
expressed as easily, or more easily, in kilopascals (kPa). This practice
seems to be growing.
I don't know the definitive answer to Gustaf's original question, but two
explanations seems likely:
(A) Those in charge of metrication were scientists and engineers with little
or no practical experience using SI in everyday life.
(B) A public-relations rationale: "English-speakers are unfamiliar with
prefixes, so we don't want to confuse them with too many. If we don't
introduce these four, they will eventually wither away and die." This
rationale seems to have backfired and turned the public against SI. And in
reality, the irregular prefixes (along with kilo and milli) have long been
taught to every American student whereas the other prefixes (e.g., mega,
giga, micro, and nano) are not routinely taught, even though they are far
more common than deci, deka, and hecto. Students are taught centimeters from
an early age and are much more comfortable with them than millimeters.
Getting rid of the irregular prefixes in areas and volumes would require
very long, impractical rows of non-significant zeroes (e.g., hm3 = 1 000 000
m3 or 0.001 km3, hm2 = ha = 10 000 m2 or 0.01 km2).
> -----Original Message-----
> From: Gustaf Sj�berg
>
> What is this idea about only using 1000-multiples?
> The cm and cL are two of the most useful units in everyday-metric system.
> The might not fit in some 1000-pattern but that is no reason to
> prevent people
> from using them. Ordinary people don't care about 1000-patterns.
> Here are som really nice and useful units that we use in Sweden
> (and Europe):
>
> Centiliters; perfect for sodacans etc. 33cL , 50cL NOT mL, they are too
> small, come in vast numbers with unecessary zeros.
> Deciliters; for cooking.
> Centimeters; always used.
> Millimeters; when centimeters are too big.
> Decimeters; in common language. ("It was only a few decimeters
> between them.")
> Hectograms; We rather say "three hectos" than "threehundred grams".
>
> The metric system has been around for over 100 years overhere and
> the units
> above are some of those that turned out to be useful. There is no
> reason not
> accepting them.
>
>
