True Fixed Width Fonts in WPF

I'm trying to parse Lab Data from an Microsoft Access Database I've already formatted all the data but text tables (Tables created with开发者_Go百科 ASCII Chars) do not display correctly. I'm using a fixed pitch font (Couier New) but the pitch seems to not be fixed when printing Underscores in markup eveything looks fine but when printing the underscored lines come up short.

The following XAML aligns correctly both on screen (in XamlPad) and on printer (HP CP2025):

  <StackPanel>
    <TextBlock FontFamily="Courier New" FontSize="30">ABCDEFGHI</TextBlock>
    <TextBlock FontFamily="Courier New" FontSize="30">A_C_E_G_I</TextBlock>
  </StackPanel>

I would check your font substitution settings on your printer.