Hi Wolfgang,
Well... because I programmed it that way.
Seriously, in the original scope, I worked on the 3 app basis. In the setup userform, I forced a use to choose three apps.
I also made another determination in the code that I would not let a user scale any of the apps down to less than 10% of the screen height/width, as I didn't want to do with the issue of having an app "open and invisible" by setting it to no height or width. I figured that would make a real mess of things, especially if it was the one with the toolbar to undo it.
One interesting point, though, is that if you only open two of the three apps you select, it will scale, but only to a max 90% on the right hand side. Now I suppose that I could alter it to allow 100% scaling if only two apps were chosen... I'll have to think on it.
FYI, I forgot to mention that at the current time this does not work with Access or Visio. Only Word, Excel, Powerpoint, Publisher and Outlook.