# Vertical line spanning fraction

I would like to write the following equation:

How do I produce the vertical line and the subscript 'iso-effect'?

-

Try

\documentclass[preview]{standalone}

\usepackage{amsmath}

\begin{document}
\begin{equation*}
\textrm{RBE}=\left.\frac{D_{\textrm{photon}}}{D_{\textrm{test}}}\right\rvert_{\textrm{iso-effect}}
\end{equation*}
\end{document}


-
The - in “iso-effect” is probably not a minus sign, but an ordinary hyphen, thus \textrm is the better choice (the same applies for “photon” and “test” as well). I would also move \left. to the left of \frac (it doesn’t change the output but is probably semantically correct). –  Qrrbrbirlbel Jan 12 '13 at 13:56
Changed. Thanks. –  hpesoj626 Jan 12 '13 at 13:59
looks to me like the "RBE" should also be \textrm. –  barbara beeton Jan 12 '13 at 17:29
@barbarabeeton Looking at the provided figure, I think you are right. Edited. –  hpesoj626 Jan 12 '13 at 17:34
Yes, RBE is not a variable. –  Eekhoorn Jan 13 '13 at 10:37