[Tex/LaTex] Thin space between minus sign and number

Question

I love the bitstream-charter font from the mathdesign package – with a small exception: The space between the minus sign and a negative number looks too cramped in my opinion.

I guess from a typographical point of view it's probably a very bad idea to mess with the font, but nevertheless my question: Is there a possibility to add a bit of space? Or steal a minus symbol from another font? Or somehow influence the kerning (but not in "1+1"-like situations)?

General requirements:

• it has to work with pdflatex
• works with siunitx
• especially aligning columns by a decimal symbol has to work

I already tried to mess around with bracketing negative numbers (based on https://tex.stackexchange.com/a/152323/36296) but this breaks the alignment in columns.

MWE

The following MWE exaggerates the shortening and the additional space to clearly see the difference.

\documentclass{article}

\usepackage{siunitx}
\usepackage[bitstream-charter]{mathdesign}
\usepackage{graphicx}

\begin{document}

    math mode $\num{-42}$: \qquad I would like a bit of space, as in $42 - 42$ 

    \bigskip

    text mode \num{-42}: \qquad ~Again I would like a bit of space and ideally a smaller minus sign to look like \scalebox{0.75}[1.0]{$-$}\thinspace42 

    \bigskip

    Bonus: aligning columns at the decimal sign should still work

    \begin{tabular}{S[table-format=1.2,round-mode=places,round-precision=2]}
            0.890888\\
         -0.505642\\
    \end{tabular}

    \bigskip

    Messing with the negative bracket breaks the alignment

    \begin{tabular}{S[%
            table-format=1.2,
            round-mode=places,
            round-precision=2,
            bracket-negative-numbers, 
            open-bracket={-\thinspace},
            close-bracket={}        
    ]}
            0.890888\\
            -0.505642\\
    \end{tabular}

\end{document}

Answer 1

Thanks to the fantastic answer of Joseph Wright this problem is solved by redefining the in-text minus symbol of siunitx:

 \cs_undefine:N \c__siunitx_minus_tl
 \tl_const:Nn \c__siunitx_minus_tl {\scalebox{0.75}[1.0]{$-$}\thinspace}

To force the usage if this symbol, the text mode of siunitx has to be used

\sisetup{mode = text}

MWE:

\documentclass{article}

\usepackage{siunitx}
\usepackage[bitstream-charter]{mathdesign}
\usepackage{graphicx}

\sisetup{mode = text}
\ExplSyntaxOn
    \cs_undefine:N \c__siunitx_minus_tl
    \tl_const:Nn \c__siunitx_minus_tl {\scalebox{0.75}[1.0]{$-$}\thinspace}
\ExplSyntaxOff

\begin{document}

    math mode $\num{-42}$

    text mode \num{-42}

    \bigskip

    Bonus: aligning columns at the decimal sign should still works

    \begin{tabular}{S[table-format=1.2,round-mode=places,round-precision=2]}
        0.890888\\
        -0.505642\\
    \end{tabular}

\end{document}