Code table 3 -- Fixed levels or layers for which the data are included
from the ECMWF publication "Binary data representation - FM 92 GRIB", May 1992

Note that octets 10, 11 and 12 from GRIB section 1 represent an Indicator of
type of level, and the Height/pressure etc of the levels. These appear in the 
output of the GRIB extraction software as "Type of level" and 
"Value 1 of level", "Value 2 of level", for example:
 Type of level (Code Table 3).              112
 Value 1 of level (Code Table 3).             0
 Value 2 of level (Code Table 3).             7


        Octet 10                Octet 11                Octet 12
Code
figure   Meaning                            Contents

00
01   Ground surface
02   Cloud base level
03   Level of cloud tops        0                       0
04   Level of O deg. C isotherm
05   Level of adiabatic condensation
06   Maximum wind level
07   Tropopause
08   \
.
.     Reserved
.
99   /
100  Isobaric surface           Pressure in hPa (2 octets)
101  Layer between two          Pressure of top         Pressure of bottom
     isobaric surfaces          in kPa                  in kPa
102  Mean sea-level             0                       0
103  Specified altitude         Altitude in metres (2 octets)
104  Layer between two          Altitude of top         Altitude of bottom
     specified altitudes        in hm                   in hm
105  Specified height level     Height in metres (2 octets)
     (above ground)
106  Layer between two          Height of top           Height of bottom
     specified height levels    in hm                   in hm
     (above ground)
107  Sigma level                Sigma value In 1/10 000 (2 octets)
108  Layer between two          Sigma value of top      Sigma value of
     sigma levels               in 1/100                bottom In 1/100
109  Hybrid level               Level number (2 octets)
110  Layer between two          Level number of         Level number of
     hybrid levels              top                     bottom
111  Depth below land surface   Depth In centimetres (2 octets)
112  Layer between two depths   Depth of upper          Depth of lower
     below land surface         surface (cm)            surface (cm)
113  \
.
.     Reserved
.
120  /
121  Layer between two          1100 hPa minus          1100 hPa minus
     isobaric surfaces          pressure of top         pressure of bottom
     (high precision)           in hPa                  in hPa
122  \
.
.     Reserved
.
127  /      
128  Layer between two          1.1 minus sigma         1.1 minus sigma
     sigma levels (high         of top, In 1/1000       of bottom, in
     precision)                 of sigma                1/1000 of sigma
129  \
.
.     Reserved
.
140  /
141  Layer between two          Pressure of top          1100 hPa minus
     isobaric surfaces          in kPa                  pressure of bottom
     (mixed precision)                                  in hPa
142  \
.
.     Reserved
.
159  /
160  Depth below sea-level      Depth In metres (2 octets)
161  \
.
.     Reserved
.
254  /