SyntheSim works well with surprisingly large models, but some models simply take too long to simulate to be used effectively in SyntheSim mode.
How long a model takes to simulate is a function of the model size, the length of the simulation, the value of TIME STEP and SAVEPER and the speed of your computer. In general if a model can be simulated in less than ½ of a second it should work reasonably well in SyntheSim mode. As a rule of thumb take the number of variables in a model as reported in Model>Settings, multiply by the number of time steps and divide by the clock speed of your computer in megahertz. If this number is less than 300 then SyntheSim will probably work quite well.
If your model is to large too smoothly respond to slider movements, you can change settings so that it will only be simulated when the mouse button is lifted, and not while the slider is being moved. To do this check the Suppress SyntheSim during slider moves checkbox on the Sketch Appearance tab of the Model Setting dialog (Model>Settings).
If your model takes more than a few seconds to simulate you may find that it is better just to perform normal simulations and not enter SyntheSim mode. Even in this case you can get some of the benefits of SyntheSim by displaying the behavior of the runs you make on the Sketch views as described in the first section of this Chapter. 
