Missing { inserted on a table

Question

I was trying to create a table, and I'm having these two following errors:

"! Missing { inserted.
<to be read again>
^
l.149 ... $n_J\cdot x_i$ & $v_j=x_j-\overline{x^'}
$ & $v^2_j$ & $n_jv^2_j$ \..."

Here's the corresponding code:

\documentclass{article} %%% use \documentstyle for old LaTeX compilers

\usepackage[english]{babel} %%% 'french', 'german', 'spanish', 'danish', etc.
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{txfonts}
\usepackage{mathdots}
\usepackage[classicReIm]{kpfonts}
\usepackage[dvips]{graphicx} %%% use 'pdftex' instead of 'dvips' for PDF output

% You can include more LaTeX packages here 


\begin{document}

%\selectlanguage{english} %%% remove comment delimiter ('%') and select language if required


\begin{tabular}{|p{0.6in}|p{0.6in}|p{0.6in}|p{0.6in}|p{0.6in}|p{0.6in}|p{0.6in}|} \hline 
\multicolumn{3}{|p{1in}|}{Messungen} & \multicolumn{4}{|p{2.4in}|}{Berechnungen} \\ \hline 
$x_j$ & $h_j\ (mm$)\newline  & $n_j$ & $n_jx_j$ & $v_j=x_j-\overline{x^'}$ & $v^2_j$ & $n_jv^2_j$ \\ \hline 
-6 & 7  & 39 & -234 & -5,9 & 34,81 & 1357,59 \\ \hline 
-5 & 12 & 66 & -330 & -4,9 & 24,01 & 1584,66 \\ \hline 
-4 & 14 & 77 & -308 & -3,9 & 15,21 & 1171,17 \\ \hline 
-3 & 24 & 133 & -399 & -2,9 & 8,41 & 1118,53 \\ \hline 
-2 & 34 & 188 & -376 & -1,9 & 3,61 & 678,68 \\ \hline 
-1 & 43 & 238 & -238 & -0,9 & 0,81 & 192,78 \\ \hline 
0 & 42 & 233 & 0 & 0,1 & 0,01 & 2,33 \\ \hline 
1 & 36 & 200 & 200 & 1,1 & 1,21 & 242 \\ \hline 
2 & 32 & 177 & 354 & 2,1 & 4,41 & 780,57 \\ \hline 
3 & 23 & 127 & 381 & 3,1 & 9,61 & 1120,47 \\ \hline 
4 & 13 & 72 & 288 & 4,1 & 16,81 & 1210,32 \\ \hline 
5 & 8 & 44 & 220 & 5,1 & 26,01 & 1144,44 \\ \hline 
6 & 10 & 35 & 210 & 6,1 & 37,21 & 302,35 \\ \hline 
\end{tabular}

\end{document}

Answer 1

In addition to fixing the immediate problem at hand (by omitting the ^ symbol in x^', you may also wish to make your table more interesting and compelling. I suggest you do so by (a) omitting all vertical lines and most horizontal lines, (b) use the line-drawing macros of the booktabs package for the few remaining horizontal lines, and (c) aligning all numbers vertically along their respective decimal markers, using the S column type of the siunitx package.

\documentclass{article}
\usepackage[ngerman]{babel}
\usepackage{amssymb,amsmath}
%\usepackage{txfonts}  % do NOT load both 'txfonts and 'kpfonts' 
\usepackage{mathdots}
\usepackage[classicReIm]{kpfonts}
\usepackage{graphicx} 
\usepackage{booktabs}

\usepackage[locale=DE]{siunitx} % for "S" column type
\newcolumntype{T}[1]{S[table-format=#1]}

\begin{document}

\begin{center}
\begin{tabular}{@{}T{-1.0}T{2.0}T{3.0}T{-3.0}T{-1.1}T{2.2}T{4.2}@{}} \toprule
\multicolumn{3}{c}{Messungen} & 
\multicolumn{4}{c}{Berechnungen} \\
\cmidrule(r){1-3} \cmidrule(l){4-7}
{$x_j$} & {$h_j$ (\si{\milli\meter})} & {$n_j$} & {$n_jx_j$} &
{$v_j=x_j-\bar{x}$} & {$v^2_j$} & {$n_jv^2_j$} \\
\midrule
-6 &  7 &  39 & -234 & -5,9 & 34,81 & 1357,59 \\
-5 & 12 &  66 & -330 & -4,9 & 24,01 & 1584,66 \\
-4 & 14 &  77 & -308 & -3,9 & 15,21 & 1171,17 \\
-3 & 24 & 133 & -399 & -2,9 &  8,41 & 1118,53 \\ \addlinespace
-2 & 34 & 188 & -376 & -1,9 &  3,61 &  678,68 \\
-1 & 43 & 238 & -238 & -0,9 &  0,81 &  192,78 \\
 0 & 42 & 233 &    0 &  0,1 &  0,01 &    2,33 \\
 1 & 36 & 200 &  200 &  1,1 &  1,21 &  242,00 \\
 2 & 32 & 177 &  354 &  2,1 &  4,41 &  780,57 \\ \addlinespace
 3 & 23 & 127 &  381 &  3,1 &  9,61 & 1120,47 \\
 4 & 13 &  72 &  288 &  4,1 & 16,81 & 1210,32 \\
 5 &  8 &  44 &  220 &  5,1 & 26,01 & 1144,44 \\ 
 6 & 10 &  35 &  210 &  6,1 & 37,21 &  302,35 \\ 
\bottomrule
\addlinespace
\multicolumn{7}{@{}l}{$N=\sum_j x_j=1{,}629$. $\bar{x}=(1/N) \sum_j n_jx_j=-0.142\approx-0.1$.}
\end{tabular}
\end{center}

\end{document}