It might be extremely simple to solve my problem, but I can't figure it out... I use the tufte-book class and I have a table inside it. In the documentation of the tufte-book class it is written that:
Any \footnotes will automatically be converted to sidenotes.
So, I tied to attach a footnote (NOT a tablenote!), which would amount to a sidenote, to one entry, but the tablefootnote package is no use, I get the error:
No counter 'Hfootnote' defined. \end{table}
This suggests that the hack with \footnotemark and manually setting the counter would not work either. Needless to say that the \sidenote command does not work either. Neither does tabularx.
My code with \sidenote does not compile at all (Minimal Non-Working Example that is...):
\documentclass{tufte-book}%
\usepackage{amsmath}%
\usepackage{amsfonts}%
\usepackage{amssymb}%
\usepackage{graphicx}%
\begin{document}
\begin{table}[htb]
\centering
\caption{Principal elementary particles}
\begin{tabular}{c||c|c|c|c} \hline
& electron & proton & neutron & photon \\ \hline \hline
symbol & e$^-$ ($\beta^-$) & p$^+$ (H$^+$) & n$^0$ & $\gamma$ \\ \hline
el. charge [C] & $-1.602176487 \times 10^{-19}$ & $1.602176487 \times 10^{-19}$ & $0$ & $0$ \\ \hline
mass\sidenote{at stand-sill} [kg] & $9.10938215 \times 10^{-31}$ & $1.672621637 \times 10^{-27}$ & $1.67492729 \times 10^{-27}$ & $0$ \\ \hline
\end{tabular}
\label{tab:PrincipalElementaryParticles}
\end{table}
\end{document}


threeparttablepackage. And since you're usingtufteyou should really also read thebooktabsdocs on table design. :-). Here's a nice example of how to use both: Add notes under the table. – Alan Munn Nov 27 '11 at 23:06