The unit codes are used in the DESCRIP0.UNITS, DESCRIP1.UNITS, DESCRIP2.UNITS, DESCRIP3.UNITS, and DESCRIP.UNITS record fields. It specifies the physical units for the data and its dimension. Each code is stored in an integer at least 32 bits long. The bits are numbered from 0 to 31, the least significant bit in the integer being number 0. Bits 29 to 31 define an index of eight possible forms of specifying units.
The format of the units code is as follows:
0 : Special and mathematical units
1 : SI base units and dimensionless units from SI base units
1 : length![]()
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2 : mass![]()
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3 : time![]()
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4 : temperature![]()
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5 : amount of a substance![]()
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6 : electrical current![]()
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7 : luminous intensity![]()
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8 : plane angle![]()
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9 : solid angle![]()
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-18 | atto | a |
-15 | femto | f |
-12 | pico | p |
-9 | nano | n |
-6 | micro | ![]() |
-3 | milli | m |
-2 | centi | c |
-1 | deci | d |
1 | deka | da |
2 | hecto | h |
3 | kilo | k |
6 | mega | M |
9 | giga | G |
12 | tera | T |
15 | peta | P |
18 | exa | E |
2 : SI approved named units
0 1 length
1 2 mass
2 4 time
3 8 temperature
4 16 amount of a substance
5 32 electrical current
6 64 luminous intensity
7 128 plane angle
8 256 solid angle
3 : General SI units in terms of base units with restrictions
4 : General non-SI units in terms of base units with restrictions
The structure of both of these forms is the same. Index 3 applies to the SI
combination of units, and index 4 applies to any combination of units that
include at least one non SI unit. There are certain restrictions in the
sizes of the various fields, depending on the number of base units that make
up the unit. Any unit that cannot be put into this form should use form 5
(General units without restrictions).
All cases have:
0 1 length
1 2 mass
2 4 time
3 8 temperature
4 16 amount of a substance
5 32 electrical current
6 64 luminous intensity
7 128 plane angle
8 256 solid angle
base num | bits | range | exponents |
1 | 15 to 19 | 0 to 31 | -16 to 16 |
2 | 12 to 19 | 0 to 15 | -8 to 8 |
3 | 11 to 19 | 0 to 7 | -4 to 4 |
4 | 8 to 19 | 0 to 7 | -4 to 4 |
5 | 10 to 19 | 0 to 3 | -2 to 2 |
6 | 8 to 19 | 0 to 3 | -2 to 2 |
7 | 13 to 19 | 0 to 1 | -1 or 1 |
8 | 12 to 19 | 0 to 1 | -1 or 1 |
9 | 11 to 19 | 0 to 1 | -1 or 1 |
base num | bits | range | |
1 | 8 to 14 | 0 to 127 | |
2 | 7 to 11 | 0 to 31 | |
3 | 7 to 10 | 0 to 15 | |
4 | 5 to 7 | 0 to 7 | |
5 | 6 to 9 | 0 to 15 | |
6 | 5 to 7 | 0 to 7 | |
7 | 7 to 12 | 0 to 63 | |
8 | 7 to 11 | 0 to 31 | |
9 | 7 to 10 | 0 to 15 |
base num | bits | range | |
1 | 0 to 7 | 0 to 255 | |
2 | 0 to 6 | 0 to 127 | |
3 | 0 to 6 | 0 to 127 | |
4 | 0 to 4 | 0 to 31 | |
5 | 0 to 5 | 0 to 63 | |
6 | 0 to 4 | 0 to 31 | |
7 | 0 to 6 | 0 to 127 | |
8 | 0 to 6 | 0 to 127 | |
9 | 0 to 6 | 0 to 127 |
5 : General units with no restrictions
0 1 length
1 2 mass
2 4 time
3 8 temperature
4 16 amount of a substance
5 32 electrical current
6 64 luminous intensity
7 128 plane angle
8 256 solid angle
These units are site-defined as specified in Section A.2.5.