Classic_paper - thanks, I possibly did not describe my problem accurately. I mostly use fluid (unless I can see WM clearly at natural light). I also have a scope, but somehow it is not helping me with the most difficult watermarks. In case of German WM 2X and 2Y there is no problems to see them clearly - usually they are very well visible even at natural light. My issue is that I cannot find the objective measure defining type X and Y. For example, on attached picture it seems that vertical size of two rectangular shapes is different, but in real life this criteria is very hard to use. So I just wonder what some other collectors using as the criteria.