\latexonly{\begin{equation} d_l = 4\,f \tan (\alpha / 2)\end{equation}}
\latexignore{\\\centerline{\emph{4 x F x tan(\alpha/2)}}}
\latexonly{This geometry is shown in figure~\ref{equilinearfig}.}
\latexonly{\begin{equation} d_l = 4\,f \tan (\alpha / 2)\end{equation}}
\latexignore{\\\centerline{\emph{4 x F x tan(\alpha/2)}}}
\latexonly{This geometry is shown in figure~\ref{equilinearfig}.}