It is critical that there be as much transparency as possible with respect to computations that underlie the variables chosen for display. In a large, integrated model, achieving such transparency is not simple. You are invited to look at the very extensive Help section called "Understanding the Model: ‘Opening the Black Box’" for extensive documentation via flow charts, equations, and computer code.
While working with display of variables, however, there are several ways in which to drill down for explanations of what lies behind their computations. After you have added variable or parameter changes to the Quick Scenario with Tree you can learn more about how a parameter or variable is generated by clicking on it and exploring the options.