A system-specific feedback control theory for fluid process control and for motion control has been developed to enable analytical tuning. The system-specific theory enables the determination of the coefficients required to implement (i.e., tune) a proportional-integral (PI) control system analytically from physical characteristics of the fluid or motion system. PI control is essentially PID control with the derivative (D) coefficient set equal to zero. (A derivative coefficient is not essential and may have a detrimental effect on system response characteristics.) System-specific theory, based on the fundamental algorithm for PID control systems, was developed from a "back-to-basics" perspective considering digital, not analog, control of fluid systems and motion systems independently. ControlProblems is an application containing numerical system models corresponding to the problems presented in Chapters 23 though 27 of this book. The problems represent typical systems that may be analyzed with system-specific PI control theory. The application enables validation of proportional integral (PI) coefficient calculations as well as investigation of system response characteristics with various PI coefficients. Numerical data for the problems is presented in the ControlProblems application. This data may be changed by the user to simulate different PI coefficients, modulated capacities, complete response intervals, signal update intervals, loads, etc. Suitability of user-specified PI coefficients may be evaluated from simulated system response characteristics. System response characteristic for default PI coefficients may be used for comparison.