How to prevent \center-column colliding with other markup?

[Risto Vääräniemi]

Hi,

I am trying to add a \center-column'ed text in my markup block.
However, that part is not properly aligned (at least in my opinion)
and it is partially placed on top of the text that's on its left side.
Should I wrap the \center-column part inside some other markup
function? I already tried \line and \column.

%%%%%%%%
\version "2.11.63"

\markup
{
    \number \override #'(baseline-skip . 0)
    {
        \line {\center-column { "7" "4" }}
        \line {\center-column {\concat {"4" "+" "3"} "4" }}
    }
}
%%%%%%%%

As you probably already guessed I'm trying to make a custom time
signature. Using a \hspace between the two columns is not a good
solution since if I change the numbers I should also change the
\hspace – I'm planning to put this inside a scheme function.

-Risto