In this chapter, we will explore the design of the graphical user interface (GUI) for pdCalc. Whenever one designs a GUI, a widget platform needs to be selected. As previously noted, I have chosen to use Qt for the creation of the GUI. That said, this is not a how-to chapter on using Qt to design an interface. Rather, I assume that the reader has a working knowledge of Qt, and the chapter itself focuses on design aspects of the GUI. In fact, as much as possible, I will refer the reader to the source code to see detailed aspects of the widget implementations. Any discussion ...