The Settings Menu

Settings->Science/Engineering Buttons: Display science and engineering buttons.
Settings->Statistic Buttons: Display statistic buttons.
Settings->Logic Buttons: Display logic buttons.
Settings->Constants Buttons: Display constants buttons.
Settings->Show All: Display all buttons available.
Settings->Hide All: Hide all extra buttons and display only standard default buttons.
Settings->Configure Shortcuts...: Configure the keyboard shortcuts used by KCalc.
Settings->Configure KCalc...: Display the KCalc settings dialog.