How can I obtain a vertical rule like the red one in the figure?
Here's the LaTeX code (without the rule):
\begin{align}\label{62}
\begin{split}
\delta_{\chi} \theta_{A} & = \mathcal{L}_{Y} \theta_{A}-2 \kappa \partial_{A} T, \hspace{1 cm} \delta_{\chi} \Omega_{AB} =\mathcal{L}_{Y}\Omega_{AB} , \\
\delta_{\chi} \lambda_{AB} & = \mathcal{L}_{Y} \lambda_{AB} + \theta_{A} \partial _{B} T+ \theta_{B} \partial _{A} T - 2 \bar{\nabla}_{A}\bar{\nabla}_{B} T,
\end{split}
\\
\label{63}
\begin{split}
\delta_{\chi} \psi_{v} & = \mathcal{L}_{Y} \psi_{v}, \hspace{2.85 cm} \delta_{\chi} \varphi_{A} =\mathcal{L}_{Y}\varphi_{A}+ \varphi_{v} \partial_{A} T+ \partial_{A} \hat{\lambda}, \\
\delta_{\chi} \psi_{A} & = \mathcal{L}_{Y} \psi_{A} + \psi_{v} \partial_{A} T + \Omega^{BC} \left( \partial_{A} \varphi_{B}-\partial_{B} \varphi_{A} \right) \partial_{C}T,
\end{split}
\end{align}
\rlap{\smash{\rule[-10cm]{0.1pt}{20cm}}}
save it as a macro and place it before the first =. Other that that a screen ruler is very handy (btw I probably got the order of the two main arguments in rule wrong) – daleif Apr 22 '18 at 11:30