# How to vertically center the \vdots in this node?

I'd like the \vdots in this chain to have the same distance to both of the arrows. I know that I could manually shift the node so that it looks right, but there must be a better solution. How?

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{chains}
\begin{document}
\begin{tikzpicture}[start chain=going below,every join/.style={->}]
\node [on chain, join] {A};
\node [on chain, join] {$\vdots$};
\node [on chain, join] {B};
\end{tikzpicture}
\end{document}

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\vdots has been designed for matrices. You can use a modified version that doesn't add space at its top:

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{chains}

\makeatletter
\DeclareRobustCommand{\rvdots}{%
\vbox{
\baselineskip4\p@\lineskiplimit\z@
\kern-\p@
\hbox{.}\hbox{.}\hbox{.}
}}
\makeatother

\begin{document}
\begin{tikzpicture}[start chain=going below,every join/.style={->}]
\node [on chain, join] {A};
\node [on chain, join] {\rvdots};
\node [on chain, join] {B};
\end{tikzpicture}
\end{document}

-