# Better way to produce V\llap{--}

Is there a better way to get the symbol produced by V\llap{--}? I need it in math mode. The symbol is someitmes used to represent volume. The above hack is not the right symbol but something close.

• How about \forall? Does it fit your requirements? – Count Zero Aug 27 '12 at 12:29
• @CountZero I need the dash to extend beyond the V. – mythealias Aug 27 '12 at 12:37
• Can you please upload (provide a link to) an image showing the desired symbol used in context? – Gonzalo Medina Aug 27 '12 at 13:05
• @GonzaloMedina the symbol is usually used when writing Reynolds transport equation. This pdf file shows it in use. – mythealias Aug 27 '12 at 17:36

\documentclass{article}
\newcommand{\volume}{{\ooalign{\hfil$V$\hfil\cr\kern0.08em--\hfil\cr}}}
\begin{document}
$\volume(abc)$
\end{document}

A better implementation, where the dash is built as above, but over a phantom V; the real one is added later, so subscripts and superscripts are placed with respect to it.

\documentclass{article}
\usepackage{amsmath}

\makeatletter
\DeclareRobustCommand{\volume}{\text{\volumedash}V}
\newcommand{\volumedash}{%
\makebox[0pt][l]{%
\ooalign{\hfil\hphantom{$\m@th V$}\hfil\cr\kern0.08em--\hfil\cr}%
}%
}
\makeatother

\begin{document}

$d\volume(abc)$

$x^{}_{\volume}$

$\volume_x$

$V_x$

\end{document}

• There are kerning issues here if you want a subscript, as in \volume_n. Also, as a differential, \mathrm{d}\volume has incorrect spacing. This issue is addressed in a solution to another question. Are there any issues with that solution? – Sandy G Jan 10 '18 at 20:15
• @SandyG The subscript problem is solved by using a phantom V in the \ooalign and a real V afterwards. Thanks for pointing to the weakness of the original macro. – egreg Jan 10 '18 at 22:48

I was looking for the same thing, but found it a bit distracting to have the cross extend beyond the lines of the V. I came up with an alternative approach:

\documentclass{article}

\usepackage{graphicx}

\newcommand{\Vol}{\rotatebox[origin=c]{180}{\ensuremath{A}}}

\begin{document}
Let $\Vol$ represent system volume.
\end{document}

Here you go. Inspired by @egreg's answer. You can adjust the position parameters in the code.

\ooalign{$V$\cr\raisebox{0.15em}{\kern0.04em--}\cr}

Another simple alternative using \makebox command with the same name of @egreg's named \volume:

\documentclass[a4paper,12pt]{article}
\newcommand{\volume}{\makebox[1pt][l]{$-$}V}
\begin{document}
$\frac{d\volume(x,y,z)}{dz}$
\end{document}

This is how to get it on Google Slides:

V\kern-0.8em\raise0.3ex-

Resulting in:

In Google Docs Addon Math equations, many of the commands, in the neat solutions provided here, are not supported: \ooalign, \raisebox, \cr, \hfill. Instead, using a simple \raise and \kern helps. This is not a generic solution that handles sub- and super-scripts. In slides, we normally want a quick solution that can be easily edited locally, and the expressions are small and local to a slide. Playing around with kern and raise can still work for sub- and super-scripts.

• This doesn't work in (La)TeX. It might work on Google Slides but that's off-topic here. – campa Jan 15 at 18:16