then measured and removed from the overall velocity by performing a second cross-correlation between the simultaneously measured Thorium-Argon (ThAr) lamp (simultaneously referring to observations where the second optical fibre illuminates the spectrograph with ThAr light) and a previously measured double ThAr observation where both fibres have been fed by light from the ThAr calibration lamp. These double ThAr measurements are generally taken every 1.5-2 hours throughout the night to continually reset the wavelength solution zero-point. These steps were discussed in @jordan14, however the overall performance in term of stability is shown in Appendix \[appendix\_stable\].

An important additional step in the calculation of the radial velocities from CORALIE is the characterisation of the offset between the data collected prior to the November 2014 upgrade of the instrument. As part of this upgrade, the CORALIE circular fibres were replaced with octagonal fibres to increase illumination stability, the double-scrambler was reintroduced into the system, and a focal mirror that focuses light on the guiding camera was replaced. Such instrumental upgrades are expected to introduce systematic offsets in the radial velocity measurements compared to pre-upgrade observations.

In an attempt to account for the offset between the CORALIE reference velocities observed before and after the 