## Contents of one observation

Data, i.e. observational parameters as well as spectra, is organized in the following way:

- One observation is self-contained. All the information needed to reduce it is recorded on the same few disk blocks. It may be one spectrum or one continuum drift.
- Each observation is divided in several sections, containing header parameters or data:
  - General information (date, times, local coordinates, sequence number, ...)
  - Positional information (source, name, astronomical coordinates, equinox, offsets, ...)
  - Spectral information (number of spectra, line names ans frequencies, resolutions, number of channels, ...)
  - Data
  - ...

In the Classic nomenclature, one observation is saved into one entry in a Classic file. Each entry is composed of an entry descriptor + the observation itself (header+intensity array). Please refer to the section The File Entries in the Classic documentation for details about the way an entry is written in the file.