BERV is the Acronym of Barycentric Earth Radial Velocity. It must be realized that the data reduction pipeline may use two different systems for the wavelength calibration of the spectrum. One is an absolute wavelength calibration system, based on recording of some Thorium Argon spectral lines delivered by a dedicated lamp. With such a system, there is no need to apply the BERV correction described below. Actually, the positions of observed narrow atmospheric lines (O2 or H2O) may be compared to the output of TAPAS, and may provide an excellent wavelength calibration of the observed spectrum, since it is taken simultaneously with the target spectrum. 
However, there are many cases when another wavelength calibration system is used in the reduction pipeline, where the original spectrum has been corrected from BERV. Therefore, all the observed atmospheric lines are shifted (rather, stretched),will not correspond to the normal output of TAPAS. Therefore, there is the option that TAPAS applies also the BERV correction to the TAPAS atmospheric lines for a good match to the observed spectrum calibrated in the Barycentric system, implying a BERV correction. 
What is BERV? Because of the rotation of the Earth around its spin axis, and because of the orbital motion of the Earth around the sun, there is a Doppler effect along the LOS (Line of Sight) affecting the observed star spectrum. The so-called BERV correction (Barycentric Earth Radial Velocity) is quite often applied to the absolute wavelength of the spectrometer, to recover the exact spectrum which would be seen if the observatory were, not on Earth, but rather at the barycenter of the solar system. Since this barycenter has a galilean motion through the galaxy, all spectra of the same star may be compared to each other even if taken at various times and dates
The BERV is the projection of the barycentric Earth +observatory velocity vector Ev on the direction of the LOS. It should be noted that it is the opposite of the radial velocity Vr =dR/dt of Earth +observatory in the direction of LOS.
It must be emphasized that the Doppler effect is not a Doppler shift of the wavelength system, but rather a Doppler stretch. A wavelength W0 of the original spectrum is seen at wavelength W1 in the spectrometer stretched by Doppler effect:<br>
<br>

W1 / W0 = (1+ Vr/c)	=(1- Berv/c)<br><br>

Therefore, if there is a BERV correction in the pipeline of the spectrometer to recover W0, 
the measure wavelength W1 has be transformed in W0 with the formula:                       <br><br>

W0 = W1 (1+ Berv/c)                                                                                <br><br>

The computed atmospheric transmission should therefore follow the same stretch to fit the wavelength scale of the star spectrum corrected in the pipeline for BERV