How do you add more space between notes?

[Scott Rippon]

I've tried searching the doco and figuring it out but haven't been able to :(

Just want to be able to add some more space between notes so that the fingering 

notation is visible.  In my below example the ukulele F chord "1" finger 

notation is hidden behind the previous C chord.

Thanks in advance.

Kind regards,

Scott Rippon.

\version "2.12.2"

\layout{

  \context{

    \Voice

    \consists "Horizontal_bracket_engraver"

  }

}

\book{

  \header{

    title = "CHORDS"

    subtitle = "Based on AMEB CPM Guitar Step 1 Advancing"

    instrument = "Ukulele G-C-E-A"

    composer = "Scott Rippon"

  }

  % C, F and G major

  \score {

    \relative c'

    {

      \override Fingering #'font-size = #-7

      \set fingeringOrientations = #'(left)

     <c e g c-3>-"C"

     <c f-\tweak #'extra-offset #'(-1 . 0)-1 f-2 a>-"F"

     <d-1 g g-3 b-2>-"G"

      \bar "|."

    }

    \header {

      piece = "C, F and G major"

    }

  }

    \new StaffGroup <<

          \relative c'

      \new Staff {

     <c e g c>

     <c f f a>

     <d g g b>

        \bar "|."

      }

      \relative c'

      \new  TabStaff {

        \set TabStaff.stringTunings = #'(+9 +4 0 +7)

        <c e g c>-"C"

        <c f f a>-"F"

        <d g g b>-"G"

        \bar "|."

      }

    >>

}