## GRIB2 - SECTION 4
PRODUCT DEFINITION SECTION

Created 05/10/05

Octet No. | Content
--- | ---
1-4 | Length of the section in octets (nn)
5 | Number of the section (4)
6-7 | Number of coordinate values after template (See note 1 below)
8-9 | Product definition template number (See Table 4.0)
10-xx | Product definition template (See product template 4.X, where X is the number given in octets 8-9)
[xx+1]-nn | Optional list of coordinate values (See notes 2 and 3 below)

Notes: 1. Coordinate values are intended to document the vertical discretization associated with model data on hybrid coordinate vertical levels. A value of zero in octets 6-7 indicates that no such values are present. Otherwise the number corresponds to the whole set of values. 2. Hybrid systems employ a means of representing vertical coordinates in terms of a mathematical combination of pressure and sigma coordinates. When used in conjunction with a surface pressure field and an appropriate mathematical expression, the vertical coordinate parameters may be used to interpret the hybrid vertical coordinate. 3. Hybrid coordinate values, if present, should be encoded in IEEE 32-bit floating point format. They are intended to be encoded as pairs.

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