STN Units System

The STN Units system was developed to support the expression of Units information for search and retrieval within STN.

The STN Units system is organized in a set of tables, corresponding to Unit Types. Within each Unit Type, the supported Units are listed. For example, the table for Unit Type = Length contains various supported length units supported by STN, such as meter, angstrom, and fathom. Where appropriate, conversion factors between the STN Units system and the SI units system are included for each supported unit.

Table of Conversion Factors

1. Conversion factors are taken from “Quantities, Units and Symbols in Physical Chemistry (IUPAC, 1988), “Conversion Tables of Units for Science & Engineering (Ari L. Horvath, Elsevier, 1986), and “CRC Handbook of Chemistry and Physics” or are calculated directly from these publications. In most cases, unit symbols are taken from the recommendations in ISO 2955- 1974 (E). For units that did not appear in this publication, symbols were taken from the IUPAC publication cited above.
   
2. Both abbreviations and the entire unit name may be used, except for multi-word units. Since spaces are not allowed in the unit symbols, multi-word unit terms do not make a lot of sense, and thus are only represented by abbreviations.
   
3. The units conversion procedure will remove a terminal “s” from a unit designation if no designation with the appended “s” can be found. Thus plurals of unit designations need to be added to the conversion table only in those cases where the plural form is not created merely by adding an “s” to the singular form.

Decimal multipliers for unit symbols are taken from the recommendations in ISO 2955-174 (E) and are listed below. Both the abbreviation and the complete name may be used. Decimal multipliers may be used with any unit symbol except for the symbols for temperature. Combinations of decimal multipliers and unit symbols that eliminate one or more of the vowels of each when combined are listed in the conversion table, e.g., micro + ohm = microhm.

Multiplier Symbol Factor by which the unit is multiplied

t, tera 1E+12 = 10**12
g, giga 1E+09 = 10**9
ma, mega 1E+06 = 10**6
k, kilo 1E+03 = 10**3
h, hecto 1E+02 = 10**2
da, deca 1E+01 = 10
d, deci 1E-01 = 10**-1
c, centi 1E-02 = 10**-2
m, milli 1E-03 = 10**-3
u, micro 1E-06 = 10**-6
n, nano 1E-09 = 10**-9
p, pico 1E-12 = 10**-12
f, femto 1E-15 = 10**-15
a, atto 1E-18 = 10**-18

Notes about these tables:

• In the following table, unit symbols are often followed by the complete name of the unit in parentheses. The text in parentheses is not part of the abbreviation.
• # after a conversion factor denotes a value that is accurate to +-5 in the rightmost digit.
• (CRC) after a conversion factor denotes a value taken from the CRC Handbook of Chemistry and Physics.

Index to Unit Types:
Acceleration
Amount of substance
Area
Computer terminology
Dynamic viscosity
Electric capacitance
Electric charge
Electric conductance
Electric current
Electric dipole moment
Electric potential
Electric quadrupole moment
Electric resistance
Energy
Entropy, heat capacity
Force
Frequency
Kinematic viscosity
Length
Magnetic field strength
Magnetic flux density
Magnetic flux
Magnetomotive force
Mass
Molar entropy, molar heat capacity
Noise intensity
Plane angle
Power
Pressure
Radiation
Solubility parameter
Temperature
Time
Velocity
Volume
Other