their associated error. We take an average of the errors in the literature as well as in the SSPP to derive the overall average external error, defined as $\langle\sigma_{\rm ext}\rangle$. We obtain $\langle\sigma_{\rm ext}\rangle$ = 0.221 dex from Equation (\[eqn:sys\]). This $\langle\sigma_{\rm ext}\rangle$ is applied to individual estimates of the SSPP-derived [\[C/Fe\]]{} to yield the total error in our measurement of [\[C/Fe\]]{} for each object by the following equation:

$$\sigma_{i,\rm tot} = \sqrt{\langle\sigma_{\rm ext}\rangle^{2} +~\sigma_{i,\rm SSPP}^{2}}.
\label{eqn:tot}$$

In the equation above, the largest contribution to the total error ($\sigma_{i,\rm tot}$) comes from the scatter ($\sigma_{\rm g}$) between our measured values and the literature values. However, if the noise increases in a given spectrum (for instance, from a low S/N spectrum), both the external and random errors contribute more to the total error.

The error bars in the lower panels of Figure \[fig:hicfe\] are obtained from the quadratic addition of our measured total error and the literature error, whereas the error bars in the upper-right panel are the total errors computed by Equation (\[eqn:tot\]). Note that, as mentioned earlier, there are some stars without properly measured errors in the literature values. For those stars, we adopt an average [\[C/Fe\]]{} uncertainty based 