The GTK user interface provides support for mouse wheels. Any window that has scroll bars can be scrolled by moving the pointer over a scroll bar and turning the mouse wheel. The drawing windows, most text windows and help viewer windows respond to the mouse wheel by scrolling when the pointer is in the window, as well as over a scroll bar (if any). In drawing windows, scrolling will be horizontal if Shift is held, and if Ctrl is held (which overrides Shift), the display will zoom in or out instead. The mouse wheel sensitivity can be changed with the MouseWheel variable.