Scene
Here you can select whether the simulation is to be calculated on the computer's main processor (CPU) or the graphics card (GPU). For sufficiently complex calculations (dense mesh, many collisions), the graphics card is always faster; the CPU can only be faster for very simple scenes. With the GPU option, the desired card can also be selected under Compute Device for systems with several graphics cards.
Note also the following Limitations
If you have selected the GPU option under Device, you can select the graphics card of your system here. If several graphics cards are available, you can then select the fastest card or the one with the largest memory, for example. If only one graphics card is available, you can ignore this setting.
This is used to set the Gravity - a force directed in the direction of the negative Y-axis. Note that a Force object 
Gravity (the direction of the force can also be changed here) can also act. Both are then added together.
This gravity also automatically acts on particles that were either created using a Liquid Fill Emitter or given a Liquid Contribution property above 0% by a Liquify Modifier.
This setting affects aerodynamic effects that can be activated in Rigid Bodies and for Cloth. In their tags, you will find the two parameters Drag and Lift in the "Forces" tab. Increase these values so that you can create aerodynamic effects such as leaves sailing through the air or flags fluttering in the wind.
The higher the Air Density, the stronger the aerodynamic effects, while an Air Density of 0 eliminates the same effects. Corresponding objects then behave as if they were in a vacuum.
In the following scene, the air density is 0, 1 and 5 (from the back left to the front right).
With this setting you can slow down (slow motion) or speed up (fast motion) all effects concerning the simulation.
Please note that the simulation changes and sometimes becomes erroneous - the more you deviate from the value 1 (=real time).
In very tiny or very large scenes, strange simulation behavior may occur (see also Tips and Tricks), such as the scene "exploding".
This factor translates the Cinema 4D size ratios into those of the underlying simulation engine. Follow the simple rule of thumb:
If you have objects flying around that are predominantly 100 C4D units in size, leave Scene Scale set to "100cm". If the objects are 1000 units in size, enter "1000cm".
You only need to change this value if strange behavior, i.e., miscalculations, occur.
If you notice that there is a delay of 1 frame when playing a simulation with generator participation (i.e. the generator is 1 frame ahead), you can activate the option here, which should improve the situation. However, the disadvantage of this is that there will then be delays of 1 frame in other areas for internal reasons (e.g. animations). In this case, you can cache the simulation and move the animation by 1 frame, for example - or also change the priority of the tag with the cache to Generator -100, for example (Simulation).
If this option is activated, the simulation always runs over the entire preview frame range as you have set using Preview Min and Preview Max (or interactively in the animation palette). Deactivate this option to define the simulation duration individually using the following two settings.
Start Frame[-2147483648..2147483647]
End Frame[-2147483648..2147483647]
Deactivate the previous option to set a custom simulation duration here. This is very practical, for example, if a swinging rope should only collide with the character at animation frame 167 - and only then should the simulation be started.
The following applies to the Simulation Scene Settings: All tags, objects and connectors relevant for a simulation end up here when it is newly created (i.e. they initially have a scene-wide effect). If you later explicitly assign tags (exception: Collider Tag) to a simulation scene object, this is removed from the list here.
The following applies to the Simulation Scene object: Drag in all simulation tags and objects that should only apply to this Simulation Scene object (see previous paragraph). These can be deactivated using the switches on the right.
Here is a small example of the Pyro Simulation System.
Given are two spheres that have been declared Emitters for smoke with Pyro Emitter Tags. Using the tag's Color option, the smoke of both objects can be colored differently, for example. You define the appearance of the smoke or even the forces that should act by adding Temperature or Fuel in the Pyro section of the Scene Settings. There you can also change, for example, the Voxel Size, which can be used to adjust the level of detail and complexity of the entire simulation.
But what if only the emitted smoke of one of the two spheres is to be calculated more coarsely or swirled differently, for example? We would need Pyro settings for this, which we could assign individually to individual Pyro Tags or Pyro Fuel Tags.
This is exactly where the Simulation Scene object with its Elements list comes into play.
On the left you can see the initial situation. Two spheres have been given Pyro Emitter Tags and emit smoke. The default values from the Pyro tab of the Scene Settings control the calculation accuracy and the calculation methods. On the right, a Simulation Scene object has been created and the Pyro tag of the left sphere has been assigned as an element. Individual settings for the smoke of the left sphere can now be made in the Pyro settings of the Simulation Scene object. Here, for example, the Voxel Size has been increased.
After calling up the Simulation Scene, drag one of the Pyro tags into the Elements list. This creates a new Pyro Output object in the scene(Pyro (Simulation Scene)), which is now linked to this Pyro tag. In addition, you will now find a Pyro tab directly on the Simulation Scene object with all simulation settings, which can now be edited individually for the linked Elements.
The existing Pyro Output object remains and is now responsible for all Pyro Emitter and Pyro Fuel tags that have not been linked in a Simulation Scene. You can recognise this Pyro Output object by its name Pyro (Default).
Now that individual pyro objects are available for the Pyro simulations, they can be used separately for computing and caching.
View of the objects in the scene. An additional Pyro Output object is attached to the Pyro Emitter Tag of sphere 2 via a Simulation Scene.