THE INTERNATIONAL SYSTEM OF UNITS
Super Units adopts the standards set forth by the International System of Units.
The International System of Units, abbreviated and commonly known as the SI, is officially known as Le Système International d'Unités and is overseen by the Bureau International des Poinds et Mesures located near Paris, France. Their website is
and their mission, as quoted from that website, is to "provide the basis for a single, coherent
system of measurements throughout the world, traceable to the International System of Units..."
The National Institute of Standards and Technology (NIST) has an excellent discussion of the SI at
http://physics.nist.gov/cuu/Units/
You may ask "How can you convert from a Swedish "aln" to a Japanese "bu" (see LENGTH) when those types independently evolved in unrelated cultures?" Well, that's where the SI comes into the scene. Each unit is converted to its SI equivalent base or derived unit (see below), and it's then easy to make the conversions.
ROUNDING
The SI makes various "rounding" suggestions for various types. You must use your
own discretion when rounding.
The SI accepts the general rounding rules. For example, if you wanted to round 83.3474882080457
to 3 digits of precision, you would round it to 83.347 since the fourth digit of precision
(4 in this case) is less than 5. If the fourth digit of precision was equal to or greater than 5, the number
would be rounded to 83.348.
Rounding is used when changing the precision on Super Units, including when the Scientific Notation
option is being used.
A BRIEF DISCUSSION OF THE SI BASE, DERIVED AND OTHER UNITS
The General Conference On Weights and Measures (called the GCPM, for
Conférence Générale de Poinds et Mesures), is an international conference attended
by scientific and engineering representatives of all the industrialized nations and various
international organizations. They have the authority to update the SI types, and their next
meeting is in 2007.
SI BASE UNITS
Seven units form the basis of the SI. Each base unit is absolute and does not
define itself in terms of other types of units. The official English SI definition for
each base unit is given below.
Base Unit Physical Quantity
1. meter Length
The meter is the length of the path travelled by light in vacuum
during a time interval of 1/299792458 s. [17th CGPM (1983),
Resolution 1].
2. kilogram Mass
The kilogram is the unit of mass; it is equal to the mass of the
international prototype of the kilogram [1st CGPM (1889), 3rd CGPM (1901)].
3. second Time
The second is the duration of 9 192 631 770 periods of the radiation
corresponding to the transition between the two hyperfine levels
(F=4, mf=0 to F=3, mf =0) of the ground state of the cesium 133
atom [13th CGPM (1967)].
4. ampère Electric current intensity
The ampere is that constant current which, if maintained in two
straight parallel conductors of infinite length, of negligible
circular cross-section, and placed 1 meter apart in vacuum, would
produce between these conductors a force equal to 2 X 10^-7 newton
per meter of length [9th CGPM (1948), Resolution 2 and 7].
5. kelvin Temperature
The kelvin, unit of thermodynamic temperature, is the fraction
1/273.16 of the thermodynamic temperature of the triple point of
water [13th CGPM (1967), Resolution 4].
6. mole Amount of Substance
(i) The mole is the amount of substance of a system which contains
as many elementary entities as there are atoms in 0.012 kg of carbon 12.
(ii) When the mole is used, the elementary entities must be specified
and may be atoms, molecules, ions, electrons, other particules, or
specified groups of such particles [14th CGPM (1971), Resolution 3].
In this definition, it is understood that the carbon 12 atoms are
unbound, at rest and in their ground state.
7. candela Luminous intensity
The candela is the luminous intensity, in a given direction, of a
source that emits monochromatic radiation of frequency 540 X 10^12
Hz and that has a radiant intensity in that direction of 1/683
watt per steradian [16th CGPM (1979), Resolution 3].
SI DERIVED UNITS
The SI also currently provides for 22 derived units that are algebraically defined in terms
of the base units.
1. radian
2. steradian
3. newton
4. pascal
5. joule
6. watt
7. degree Celsius
8. coulomb
9. volt
10. farad
11. ohm
12. siemens
13. weber
14. tesla
15. henry
16. lumen
17. lux
18. hertz
19. becquerel
20. gray
21. sievert
22. katal
Combinations and/or multiples of a base or derived unit also constitute a derived type.
For example, "meter cubed" and "volt per meter" are considered derived types.
The SI defines types in the singular, so something like "volts per meter" would not
be used.
OTHER TYPES OF PERMITTED UNITS
The SI currently permits the use of other unit types, i.e., the degree, arcsecond, minute,
etc. in lieu of a Base or Derived type, but strongly discourgages any such use. SUPER UNITS only uses approved Base or Derived types as the basis for each category.