Overlook of Leevi is quite different than those pieces of software that are common in X11 displays. Leevi does not use any existing user interface library, like GTK or QT, but it's own implementation instead. The reason for this is that I am not very keen to use any of those common libraries for constructing user interfaces, as they are all the same: Grey square windows with some grey boxes in it (menues, buttons, lists etc) and a lot of text in every box. Whatsmore, they are all lacking good widgets to use with software like Leevi. I personally feel like I am filling up some social service application when I use software built on GTK for example, and I tried to avoid that when I was designing the Leevi's interface and widgets for it. I wanted it to look and feel like real device.
Using knobs and buttons
Mouse with wheel is highly recommended. Each widget (knob, switch etc.) can be driven by just moving the mouse pointer over the widget and then adjust the widget with mouse wheel. You dont have to click anything, just move and roll. Actually, it is impossible to use Leevi without some kind of pointing device, as keyboard shortcuts for widgets does not exists.
Knob widget can be finetuned by pressing either left or right mousebutton. Right click makes widget value to increase by one step, while left click decreases widget's value by one.
Knob widgets can also adjusted by clicking a small dot in widget's scale, especially useful if you want to tune knob from minimum to maximum value at once.
There is also menues attached in knobs with beak, menu can be activated by pressing second (middle) mouse button in top of beaked knob widget. Once the menu is active, menu item can be selected with first (left) or second (middle) mouse button, third (right) mouse button cancels the menu.
Moving main window
Main window can be moved around my pressing either Tab or Backspace key along with first (left) mouse button and by moving the mouse. This is useful especially if you are using Leevi in borderless mode (use -e commandline switch to enable borderless mode).
Failure lamp will light if there are some problems communicating with the device. Usually this means that device does not accept commands and they will timeout continuously. In case that failure light is on, it is wise to quit Leevi, restart your device, and start Leevi from console so you are able to see its output for possible errors. Please also check Leevi's -io and -wo commandline switches to print info and warning messages to standard output.