# Imposing similar heights for boxes using \parbox

I am trying to impose similar heights for 2 different boxes. I am trying to use \parbox but this doesn't work very well since the boxes have still different heights :

\documentclass{beamer}

\usepackage{fancybox}

\begin{document}

\begin{frame}
\begin{equation*}
\ovalbox{\parbox[b][0.75\baselineskip]{0.5\linewidth}{$\nabla \zeta_0 = -\frac{\delta r}{h^{*}} \ \text{avec :}\ \frac{1}{h^{*}} = \frac{1}{\alpha h_p} - \frac{1}{H}$}
}
\
\ovalbox{\parbox[b][0.75\baselineskip]{0.5\linewidth}{$\alpha = 1 - \frac{n}{n'} \ \text{et :} \ h_p = h_0$}
}
\end{equation*}
\end{frame}
\end{document}


What am I missing here ? Thank you in advance,

• Replace position b (bottom) by c (center)
• increased height a little bit (using 1 \baselineskip)

### Result ### Code

\documentclass{beamer}

\usepackage{fancybox}

\begin{document}

\begin{frame}
\begin{equation*}
\ovalbox{\parbox[c][\baselineskip]{0.5\linewidth}{$\nabla \zeta_0 = -\frac{\delta r}{h^{*}} \ \text{avec :}\ \frac{1}{h^{*}} = \frac{1}{\alpha h_p} - \frac{1}{H}$}
}
\
\ovalbox{\parbox[c][\baselineskip]{0.5\linewidth}{$\alpha = 1 - \frac{n}{n'} \ \text{et :} \ h_p = h_0$}
}
\end{equation*}
\end{frame}
\end{document}


As already said for your previous question, hf-tikz is more powerful, including options to specify the height:

\documentclass{beamer}

\usepackage[beamer,customcolors,nofill]{hf-tikz}
\hfsetbordercolor{black}

\begin{document}

\begin{frame}
\begin{equation*}
\tikzmarkin<1->{a}(0.1,-0.4)(-0.1,0.6)
\nabla \zeta_0 = -\frac{\delta r}{h^{*}}  \ \text{avec :}\ \frac{1}{h^{*}} = \frac{1}{\alpha h_p} - \frac{1}{H}
\tikzmarkend{a}
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