[Tex/LaTex] How to Specify Intermediate Font Sizes in Koma-Script

fontsizekoma-script

According to the KOMA-Script manual,

the KOMA-Script classes offer the feature of selection of any desired size for the main document font. In this context, any well known TeX unit of measure may be used and using a number without unit of measure means pt.

The default Koma Script font size is 11 points. I can specify 8 points without any difficulty, but if I try 8.5 I get the following error message

LaTeX Warning: Unused global option(s):
    [8.5pt].

And the text reverts then to the default 11 point size. So how do I specify intermediate point sizes in KOMA-Script?

To respond to Johannes_B comment, I tried this:

\documentclass[fontsize=8.5pt,paper=a6,pagesize]{scrbook} 
\KOMAoption{fontsize}{8.5pt}
 %if set here, you need to:
\recalctypearea 
\usepackage{fontspec,xltxtra,xunicode}
\defaultfontfeatures{Mapping=tex-text}
\setromanfont[Mapping=tex-text]{Minion Pro Cond}
\usepackage{blindtext} 
\begin{document} 
\blindtext 
\end{document}

The error message received was:

LaTeX Font Warning: Size substitutions with differences
(Font)              up to 0.5pt have occurred.

It is kind of strange that you would have to specify the font size twice; but OK.
But more importantly, if size substitutions merely drop the font back to 8 pt. or pump it up to 9pt, then you really don't have access to intermediate point sizes in Koma-script. Or?

(second edit) Why is this syntax OK:
A. \documentclass[8pt]{scrbook}
but this not?
B. \documentclass[8.5pt]{scrbook}

I deleted the pagesize code because it's not relevant (except with respect to the calculation of the type area).
In Example A there is no "fontsize=8pt" declaration, yet the class produces 8 pt typesetting.
Example B yields the previous error (i.e., global option ignored) while adding "fontsize=8.5" yields an error message that the font size may be substituted (how would you know?) with differences of up to .5 pt (up or down or both?).

Best Answer

Just to have the code properly:

The warning is very clear, you are using an option that is not defined. Set the fontsize the way it is supposed to be. If you are not setting it globally (as an option to documentclass) but at a later point using \KOMAoption{fontsize}{4pt} you need to tell package typearea to recalc the typearea.

\documentclass[
fontsize=8.5pt,
paper=a6,
pagesize
]{scrartcl}
%\KOMAoption{fontsize}{8.5pt}
%\recalctypearea
\usepackage{blindtext}
\begin{document}
\blindtext
\end{document}

But you need to be aware of something: Just because you can request a font of any given size, you need to have that size available. If not, LaTeX will fall back to the next matching available font size.

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