Two column equation block with vertical separator

Question

I have seen various examples in text books and web pages (like here) of two column equation blocks, where the left column has some equation(s) and the right column has some explanation on variable meanings and/or other things. I wish to split an equation like below into two columns with a vertical separator in between without involving minipage, Tikz, and other fancy stuff like that. Seems like something that should be in common demand. But I cannot find an example of it. Any help would be greatly appreciated.

\begin{flalign}
z &= \frac{R\left(S_2 − S_1\right)}{2\left(S_1 + S_2\right)} + \frac{R}{2}\\
text{\scriptsize{where}}
    &\text{\scriptsize{ $R$ is the camera range,}} \nonumber\\
    &\text{\scriptsize{$S_1$ is the amount of the light pulse received, and}} \nonumber\\
    &\text{\scriptsize{$S_2$ is the amount of the light pulse blocked \cite{medina1992three} \nonumber.
}}
\end{flalign}

I am using the scrbook documentclass.

Answer 1

You can use a | delimiter and an array

% arara: pdflatex

\documentclass{scrbook}
\usepackage{blindtext}
\usepackage{mathtools}
\usepackage{array}

\begin{document}
\blindtext
\begin{equation}
    z = \frac{R(S_2 − S_1)}{2(S_1 + S_2)} + \frac{R}{2} \quad \left|\quad\begin{array}{r@{\ }>$l<$}
    R   & is the amount of the light pulse received, and\\
    S_1 & is the amount of the light pulse received, and\\
    S_2 & is the amount of the light pulse blocked [MED92]\\
\end{array}\right.
\end{equation}
\begin{equation}
    z = \frac{R(S_2 − S_1)}{2(S_1 + S_2)} + \frac{R}{2} \quad \left|\quad\begin{array}{>$l<$}
    $R$ is the amount of the light pulse received, and\\
    $S_1$ is the amount of the light pulse received, and\\
    $S_2$ is the amount of the light pulse blocked [MED92]\\
\end{array}\right.
\end{equation}
\blindtext
\end{document}