# Fix ugly kerning in equation subscript

I'm beautifying some HW solutions for the upcoming semester, and came across a kerning issue

\documentclass[]{article}
\usepackage{amsmath}
\begin{document}
$C_{in} \ \ C_{out} \ \ C_{eff}$

\end{document}

The output:

The "in" and "out" subscripts look fine, but "eff" seems very spread out. Is there a quick fix?

• That’s because the eff is interpreted as e times f times f, and the same goes for in and out. So you should either use the \mathit by @Sebastiano in the answer, or \mathrm, or \text, etc. – Ruixi Zhang Aug 27 '18 at 20:44
• @RuixiZhang My thoughts exactly. – Dr. Manuel Kuehner Aug 27 '18 at 20:45

$C_{\mathit{in}} \ \ C_{\mathit{out}} \ \ C_{\mathit{eff}}$
$C_{\mathrm{in}} \ \ C_{\mathrm{out}} \ \ C_{\mathrm{eff}}$
$C_{\mathbf{in}} \ \ C_{\mathbf{out}} \ \ C_{\mathbf{eff}}$