Keywords: class-spectral-axis-v12

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## The header parameters

Table: `CLASS` header parameters used to describe the frequency/velocity axes and their translation in this document.
`CLASS` name | Unit | Translation | Notation
`nchan` | -- | Number of channel | --
`rchan` | -- | Reference channel |
`restf` | MHz | Tuned signal rest frequency |
`image` | MHz | Tuned image rest frequency |
`fres` | MHz | Observatory channel spacing |
`vres` |  | Velocity channel spacing |
`voff` |  | source systemic velocity |
`doppler` | -- | Doppler factor |

Table describes the `CLASS` header parameters used to describe the frequency/velocity axes and their translation in this document. The signal and image frequency axis are given in the source (rest) frame by

| (35)

and

| (36)

with

| (37)

where is the frequency channel spacing , and is the source systemic velocity in the measurement frame. The corresponding velocity axis in the measurement frame is thus given by

| (38)

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