The previous equations assume that the systemic velocity is given in the same frame as the frequency channel spacing. However, at the 30m the systemic velocity is usually given in the LSR frame (as requested by the user) and the channel spacing and the doppler factor are given in the observatory frame.
On one hand, the rest frequency scale is correctly computed by CLASS because the channel spacing and the doppler factor are given in the same frame. On the other hand, the velocity scale is only approximated because the source systemic velocity is given in another frame, most often the LSR frame.
The end-user (astronomer) is interested with the velocity scale in the LSR
frame
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The easiest way out of the problem would be to write the parameters of the
header in the LSR frame in the calibration software that writes the CLASS
observation with
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*************************************************************************** Question: What about the image frequency? Should it be changed as in the case of the MODIFY VELOCITY command? ***************************************************************************