at recovering the true velocity (see Section \[s:cahk\]), we see that the red component, corresponding to Ca H&K, has a measured velocity range similarly small to that of the [Si$\,$]{} features noted above. Specifically, the maximum difference of measured Ca H&K velocities over all temperatures probed is only 290 [kms$^{-1}$]{}. However, the measured velocity for the [Si$\,$]{} $\lambda 3858$ feature changes significantly with temperature. Over the full temperature range probed, the measured [Si$\,$]{} $\lambda 3858$ velocity ranges from $-15$,550 to $-19,$380 [kms$^{-1}$]{} – a difference of 3820 [kms$^{-1}$]{}, or roughly an order of magnitude greater than that of the other features.

A single-Gaussian fit performs even worse. Because of the changing [Si$\,$]{} $\lambda 3858$ velocity and its varying strength, a single-Gaussian fit to the Ca H&K feature results in a  range of $-13$,250 to $-17,670$ [kms$^{-1}$]{} over our chosen temperature range for a maximum difference of 4420 [kms$^{-1}$]{}. Since the  measured using a single Gaussian can have dramatic differences even when there is no change in physical velocities, this is even more reason to avoid this technique.

Figure \[f:spar\] also shows the [Si$\,$]{} $\lambda 5972$ to [Si$\,$]{} $\lambda 6355$ ($\mathcal{R}$(Si)) and [Si$\,$]{} $\lambda 3858$ to Ca H&K ratios, which we 