[Tex/LaTex] \label is forcing roman numerals into arabic numbers

Question

I am trying to put a caption and label on a table for a lab report. My professor insists that we use roman numerals for tables e.g. (Table IV). But the \label command is forcing 'IV' into '4' when I compile (using XeLaTeX).

Also, I am having trouble putting a Greek letter into the main text. I am using \sigma and it gives me the error Missing $ Inserted.

Here's my code for the roman numerals:

\begin{table}[!ht]
\begin{tabular}{ |c||c|c|c|c| }
 \hline
 \multirow{2}{*}{Samples} &
  \multicolumn{2}{c|}{GFRP} &
  \multicolumn{2}{c|}{CFRP} \\
 & MOR Eq.3 (ksi) & MOR Eq.4 (ksi) & MOR Eq.3 (ksi) & MOR Eq.4 (ksi)\\
 \hline
 1 & 86.38 & 68.50 & 65.42 & 79.98 \\
 2 & 78.17 & 61.25 & 66.45 & 80.46 \\
 3 & 78.55 & 63.18 & 69.19 & 88.01 \\
 4 & 62.40 & 53.15 & 66.46 & 78.68 \\
\hline
\hline
 Average & 76.37 & 61.52 & 66.88 & 81.78 \\
 Std. Dev & 10.05 & 6.37 & 1.61 & 4.22 \\
 \hline
\end{tabular}
\caption{The average thicknesses and widths as well as standard deviations of the samples.}
\label{table: IV}
\end{table}

Answer 1

To change the table numbering to roman you just need to redefine the command \thetable which prints the table counter. So you make use of \Roman{<counter>}. For small letters you can use \roman{} instead (but it is ugly for captions).

\documentclass[11pt,a4paper]{report}

\renewcommand{\thetable}{\Roman{table}}

\begin{document}
\begin{table}\centering
contents
\caption{content...}
\label{tab.foo}
\end{table}
In Table~\ref{tab.foo}
\end{document}