# Part 3 - Technical Appendices

This portion of the Guide provides technical information regarding the software.

The topic of Chapter 12 is DT, the time interval between calculations in the software. In Chapter 12, you'll learn more about what DT is, and how it is used. You'll be provided with a set of practical guidelines for choosing an appropriate value for DT in your models.

Chapter 13 discusses the simulation algorithms employed by the software. In this Chapter, you'll learn how the software does its internal calculations under the Euler, 2nd-order Runge-Kutta, and 4th-order Runge-Kutta integration methods.

Chapter 14 looks at the internal rules of grammar used by the software. In Chapter 14, you'll learn about topics such as prioritization rules for non-negative stocks and allowable stock-flow connections.

Finally, in Chapter 15 you'll find answers to frequently asked questions and a range of techniques that will help you optimize performance and troubleshoot problems in your models.

The Chapters in this part of the Technical Documentation are designed to be used as reference material. You may want to skim the Chapters now. Then, when you need an in-depth technical treatment of one of the topics covered, take some time to work through the appropriate Chapter.