Seeing the look of my Calibre, üeriod IS the decimal separator. But I still can't understand why in Calibre I got the zeros once behind and once before the separator. I am quite sure that I created the column exactly the way of capinks example:
But one es confusing, which might make comma the separator: In the Calibre list I see it only this way "Series [number]" but if I open a book to change Metadata, in the "number"-Field there is always a number with ",00" (Komma Zero Zero). So I'll try to modify the column the way chaley adviced. Thanks for this new try!