I have been debugging and testing it all over again, found some loose ends, but I think I have got them all now.
I know I used lots of code, so I guess I have to change that at some point in the future.
– edit – Except for the extensive code, all issues are solved now (99.9% sure).
You can do all arethmetic operations with the 0.xxx or just .xxxx in my calculator.
You also can do all kind of operations with the minus 3x-2=-6
Perhaps I should add the zero to make it neat and clear.