Documentation/FAQ/Writer/AutomaticFunctions/The meaning of Single Spacing
Most of the line spacing possibilities for paragraphs in Writer lie on top of the "single spacing" concept, which is not wrong by itself... The problem is that "single spacing" is not defined on the help: it only says "Applies single line spacing to the current paragraph. This is the default setting".
For Linux Libertine font, and considering that a "point" (the standard unit used to measure fonts) is 1/72 of an inch, if you plot the line spacing as a function of font size (both measured on the same units), you will obtain a perfect linear regression with a 1.18 coefficient: that means "single spacing" is a distance 18 % larger than vertical font size.
For example: if you take a 12 points fonts, change that into centimetres (0.42333 cm) and multiply it by 1.18 you will get ~ 0.5 cm.
This "coefficient" could be slightly different for different typefaces.
This linear relation between font size and line spacing is non-standard: usually small and large fonts needs larger line spacing than "mid sized" fonts.
