After some brute-force attempts I found out that I could right-align two lines in a longtabu cell as follows:
\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[utf8x]{inputenc}
\usepackage{booktabs}
\usepackage{longtable}
\usepackage{tabu}
\usepackage{xcolor}
\begin{document}
\newcommand{\desc}[2]{ \begin{minipage}[t]{6em} \hfill \textbf{#1}\\ \footnotesize \raggedleft #2 \end{minipage} }
\begin{longtabu} to \linewidth{r l}
\desc{Frequency}{kHz} & \bfseries Callsign \\ \toprule
\endhead
2500 & WWV \\
3330 & CHU
\end{longtabu}
\end{document}
When I change the second line to use \hfill it is aligned to the left:
\newcommand{\desc}[2]{ \begin{minipage}[t]{6em} \hfill \textbf{#1}\\ \footnotesize \hfill #2 \end{minipage} }
And if I try to use \raggedleft for the whole minipage, like this:
\newcommand{\desc}[2]{ \begin{minipage}[t]{6em} \raggedleft \textbf{#1}\\ \footnotesize #2 \end{minipage} }
then the document does not compile anymore. Why not? In any Office program I would just select the cell content and press the “right aligned” button, is LaTeX really that complicated?
