Legacy font dimensions in TeX

tex-legacy-fontdimens.tex

\documentclass{article}
\usepackage{booktabs}
\begin{document}
\def\XeTeX{XeTeX}
\def\cs{\texttt{\char`\\}}
\centerline{%
\begin{tabular}[t]{@{}lp{4cm}@{}}
\toprule
\multicolumn{2}{@{}c@{}}{Text fonts} \\
\midrule
$\phi_1$ & slant per pt                \\
$\phi_2$ & interword space             \\
$\phi_3$ & interword stretch           \\
$\phi_4$ & interword shrink            \\
$\phi_5$ & x-height                    \\
$\phi_6$ & quad width                  \\
$\phi_7$ & extra space                 \\
$\phi_8$ & cap height (\XeTeX\ only)   \\
\bottomrule
\end{tabular}
\quad
\begin{tabular}[t]{@{}lp{4cm}@{}}
\toprule
\multicolumn{2}{@{}c@{}}{Maths font, \cs{fam}2} \\
\midrule
$\sigma_5$    & x height                    \\
$\sigma_6$    & quad                        \\
$\sigma_8$    & num1                        \\
$\sigma_9$    & num2                        \\
$\sigma_{10}$ & num3                        \\
$\sigma_{11}$ & denom1                      \\
$\sigma_{12}$ & denom2                      \\
$\sigma_{13}$ & sup1                        \\
$\sigma_{14}$ & sup2                        \\
$\sigma_{15}$ & sup3                        \\
$\sigma_{16}$ & sub1                        \\
$\sigma_{17}$ & sub2                        \\
$\sigma_{18}$ & sup drop                    \\
$\sigma_{19}$ & sub drop                    \\
$\sigma_{20}$ & delim1                      \\
$\sigma_{21}$ & delim2                      \\
$\sigma_{22}$ & axis height                 \\
\bottomrule
\end{tabular}
\quad
\begin{tabular}[t]{@{}lp{4cm}@{}}
\toprule
\multicolumn{2}{@{}c@{}}{Maths font, \cs{fam}3} \\
\midrule
$\xi_8$    & default rule thickness      \\
$\xi_9$    & big op spacing1             \\
$\xi_{10}$ & big op spacing2             \\
$\xi_{11}$ & big op spacing3             \\
$\xi_{12}$ & big op spacing4             \\
$\xi_{13}$ & big op spacing5             \\
\bottomrule
\end{tabular}
}
\end{document}