diff --git a/doc/sgpem2uman.texi b/doc/sgpem2uman.texi
index c8fd4a6..ea27b93 100644
--- a/doc/sgpem2uman.texi
+++ b/doc/sgpem2uman.texi
@@ -944,6 +944,47 @@ button of the dialogis pressed.
 @cindex simulation
 
 
+The simulation itself is not interactive, so it may be thought as a recording.
+
+From a mathematical point of view, every simulation has an instant, called 
+its @strong{end}, after wich no significant changes invove the simulated entities.
+Our simulator does reproduce simualations from the beginning to the end, 
+and not further.
+
+
+@subsubsection Simulation reproduction controls
+
+Controls over the simulation reproduction are very similar to those of a 
+digital audio player.
+
+The "play" button starts the reproduction, the "pause" button pauses it, and
+the "stop" button stops it. After the simulation is stopped, the last reproduced
+information is left on the screen, as if the simulation were paused. Anyway, 
+pressing play after having stopped the simulation will start the reproducion from 
+the beginning of the recording.
+
+
+@subsubsection Simulation reproduction modes
+
+If the simulation play mode is set to @strong{continuous}, reproduction of the simulation 
+will continue until the end is reached.
+Otherwise the simulation will pause after every single advance in reproduction.
+The simulation mode may be selected on the "Simulation" menu.
+
+
+@subsubsection Caching issues
+
+The content of the simulation itself is calculated on demand, and cached, so
+the first reproduction will usually be slightly slower than the following ones.
+
+When a simulation is stopped the cache is @strong{not} erased. The cache is erased
+each time the user @strong{modifies} the simulated environment, by adding, 
+removing or editing any kind of entity, or by changing any policy or any of 
+its parameters.
+
+This is also the reason for simulations using the lottery policy will sometimes 
+be reproduced identical.
+
 @c % -------------------------------------------------
 @node From the commandline, (none), From the GUI, Using SGPEM
 @section From the commandline