The problem with KDE is: It overwhelms the user with irrelevant / trivial / unneeded "help" documentation, yet as soon as someone has a real question, the HELP button is next to useless. Case in point: What does the CTRL key in KCalc do ? Answer: it shows current key binding, i.e. which key on a hardware-keyboard does what function. Is that self-explanatory ? No, not at all, much like CTRL-2 does sth. else unrelated, so does SHIFT. Where does one find this info ? Somewhere one the web where no one looks for it. Where do we NOT find it, as usual, and therefore gave up all hope? Of course, in KDE HELP can we not find it, the "HELP" with the red/white floating-device that has a lot of uninteresting things to say.
Where is this info missing on https://docs.kde.org/trunk5/en/kdeutils/kcalc/index.html resp. how and where would you add mor info "Control-key = key bind"?
OK it - indeed - is there in KHelpCenter, but the "what is this" function is of rather little utility inKCalc.