How to add a calculator to the multiwindow on a galaxy tab s 10.5; is there a fine point stylus?

[AC Question]

I would like to be able to multi task with a calculator, but there isn't one in the multi window tray on my galaxy tab s 10.5. How do I add one to the tray? And I prefer to use a fine point stylus with the s note app I downloaded on my Tab S 10.5, is there one available?