large room for improvement
This calculator has so much potential, as far as I can see! It is such a pity that it has not been designed with any other user in mind, apart from the developer himself!
There are two (usually implicit) goals in writing a manual for a sofware one has developed.
One, let's call it «the generous goal», is to help as many potential users feel at home with most of the application functionality.
The other goal, let's call it «self-afirming one», is for the developer, to bask in the limelight of his professionalism. Such a manual is not written for potential users, but for fellow developers, in some sort of professional competition among developers. It is similar to radio short wave afficionados, train spotters, and other hobbyists. The more obscure the hobby is, the higher the compulsion in bragging with one's own expertise.
Sadly, most German-speaking developers are of the second kind, so their manuals are useless (at least for potential users).
What a pity!!
To preempt misunderstandings: I have studied mathematics myself in Heidelberg, so I might have some idea about maths.
What I criticise here is the developer's reluctance of making this application easy to use.