# Nomenclature reminder

It is reminded that:

1. A CLASS observation is used to store and retrieve a flux array for analysis into CLASS. This flux array is called RY hereafter.
2. In a CLASS observation, there are 3 ways to define the X axis associated to RY:
   1. the spectroscopic section for regularly sampled (in frequency and velocity) spectroscopic data,
   2. the drift section for regularly sampled (in time and angular position) continuum drift data,
   3. the so-called "X coordinate section" for irregularly sampled spectroscopic or continuum drift data.
   One of these 3 sections is used to define the RX array describing the X axis associated to RY. In the cases (a) and (b), RX in memory is built so that it has as many values as RY. In the case (c), the CLASS Data Format ensures that RX has as many values as RY. For simplicity hereafter, we call RX the X axis coming from one of these sections, and Nchan its number of values.