double time signatures

[Martin Kemp]

Dear All

I have nearly got what I want with the following snippet but can't 
currently centrally align 12 over 8 (12/8). Any help gratefully 
apprecitated.

best

Martin

<<
#(define ((double-time-signature glyph a b) grob)
   (grob-interpret-markup grob
   (markup #:override '(baseline-skip . 2.5) #:override '(fontsize . 
4)  #:number
   (#:line ((markup (#:fontsize 2 #:musicglyph glyph))
   (#:fontsize 0 #:column (a b)))))))

music = \relative c' {
\override Score.TimeSignature #'stencil =
    #(double-time-signature  "timesig.C44" "12" "8")
\time 3/4
c8 b c d e f g4 g g g4 a8 g f e d2. \bar "|."
}
\score { \music }
>>