This chapter will help you to understand the nuances of simulation engine settings that not only affect the accuracy of calculations but also affect the run time of a model. This becomes very important especially for large building models. Three concepts covered in this chapter are time step, which may be treated analogous to the least count of the model; method of calculation for energy balance; and the algorithm for convective heat transfer in various building components. Simulation tools offer freedom to choose a smaller time step at the cost of a significant increase in run time. Similarly, the calculation method and convection algorithm are also associated with the accuracy of calculation at the cost of run time. These tutorials help in understanding the methods as well as the extent of difference that is obtained in the results when using different approaches. This information can be useful to the simulator to decide the appropriate simulation setting as per the availability of computing power, time and requirement of accuracy.