To open configruation for kcalc press :kbd:`Control+Shift+ +` or :menuselection:`Settings --> Configure Kcalc`. To change the maximum number of digits change the :guilabel:`Maximum number of digits` field. If you want to show the result in the window title check the :guilabel:`Show result in window title` checkbox.
The :guilabel:`Font` tab has settings to change settings with your fonts. To choose the font for your buttons on your calculator :guilabel:`Button font` and press the :guilabel:`Choose` button to the font for the buttons on your calculator. To change the font for the diplay of the calculator. :guilabel:`Display font` will change how the and the :guilabel:`Choose` button
