Hi Jimmy and David.
Thanks again for your answers.
I have now tried to compare some other books and with some other tools.
For instance...
With the plugin Jean-Paul-Sarte's Nausea gives me 90 in FK Readability Score as an Epub file (with deleted cover and index) and 87 if I convert the file into txt-format.
When I use
http://flesh.sourceforge.net I get the score 76.6.
When I use
https://www.online-utility.org/engli...nd_improve.jsp I get the score 73.06
When I use
http://www.checktext.org I get the score 74.6
The plugin does seem to rank books that is hard to read lower on the scale. I think this example with Saatre and the examples from yesterday with Murakami and Bukowski proves that. Plus when I put in Gunter Grass' The Tin Drum I got 60 and that book has some extremely long sentences.
But it seems to measure the Flesch-Kincaid readability too high compared to other tools.
Changing the column to floating did help the decimal issue. Thanks!