I worked hard to find a MWE for this issue, stripping out just about everything from my preamble and my SAE class file until I discovered that it seems the siunitx package does not play well with the times font (it works fine with Helvetica).
I'll start with an MWE of my class file, in which I have forced the times font to comply with SAE guidelines and their template files:
\NeedsTeXFormat{LaTeX2e}
\ProvidesClass{saeRyan}[2016/02/23 SAE Technical paper format^^J]
% Option for the "Times New Roman" font
\DeclareOption{times}{%
\renewcommand{\familydefault}{ptm}%
\typeout{^^JSetting document font to Times^^J}%
}
% Option for letter size paper (U.S.)
\DeclareOption{letterpaper}{%
% Define the margins for letter size paper (0.5" margins all the way around) using the geometry package.
\PassOptionsToPackage{letterpaper,nohead,left=.5in,top=.5in,right=.5in,textheight=10in}{geometry}%
\typeout{^^JPaper size: Letter^^J}%
\AtBeginDocument{ \columnsep .5in }
}
\DeclareOption{pdftex}{%
\PassOptionsToClass{\CurrentOption}{article}%
\PassOptionsToPackage{\CurrentOption}{geometry}
}
\DeclareOption{nonumber}{%
\pagestyle{empty}%
}
% This handles any options that are not understood by the class.
\DeclareOption*{\typeout{^^JOption [\CurrentOption] not supported by this style.^^J}}
% Default Options
\ExecuteOptions{times,letter,9pt}
\ProcessOptions
% The extarticle class allows for 9 pt font as the normalsize font.
\LoadClass[twocolumn,9pt]{extarticle}
Now here is a MWE of the issue I'm having with using this minimum class file:
\documentclass[letterpaper]{saeRyan}
%\usepackage{lmodern}
\usepackage[detect-all]{siunitx}
\usepackage{enumitem,booktabs,cfr-lm}
\usepackage{tabularx}
\usepackage[referable]{threeparttablex}
\renewlist{tablenotes}{enumerate}{1}
% This package is for convenience in making notes during the revision process.
%\usepackage[colorinlistoftodos]{todonotes}
\begin{document}
\begin{table}[h]
\footnotesize
\centering
\begin{tabular}{ll}
\toprule
times vs. helvetica using siunitx: & \SI{110}{\micro\meter} 110 micrometers (correct font)\\
\bottomrule
\end{tabular}
\caption{Font Test}\label{tab:test}
\end{table}
\end{document}
You can see what the problem is here... despite siunitx having the detect-all switch in there, the unit of siunitx is helvetica while the rest of the document is times. This makes for some weird looking units throughout the document (not just in tables). Anybody see an obvious problem? I really don't know much about writing class files, I'm just trying to pick things up as I go.