Index: src/sas/sasgui/perspectives/fitting/media/fitting.rst
===================================================================
--- src/sas/sasgui/perspectives/fitting/media/fitting.rst	(revision c926a9787e05478bd241a391873fc259e32825d6)
+++ src/sas/sasgui/perspectives/fitting/media/fitting.rst	(revision 332c10d1c6175b2c32df6a23f58184feaef866d8)
@@ -17,6 +17,10 @@
    Smearing Functions <resolution>
 
+   Fitting Models with Structure Factors <fitting_sq>
+
+   Writing a Plugin Model <plugin>
+
    Polarisation/Magnetic Scattering <magnetism/magnetism>
-   
+
    Oriented Particles <orientation/orientation>
 
@@ -27,6 +31,4 @@
    Fitting SESANS Data <sesans/sesans_fitting>
 
-   Writing a Plugin Model <plugin>
-
    Computations with a GPU <gpu_setup>
 
Index: src/sas/sasgui/perspectives/fitting/media/fitting_help.rst
===================================================================
--- src/sas/sasgui/perspectives/fitting/media/fitting_help.rst	(revision 8b893964adb6b330d7638d1e9692c0aacf81a9b6)
+++ src/sas/sasgui/perspectives/fitting/media/fitting_help.rst	(revision fa307ddb8d25a41b44c02bd525f9727d5b4b7e5b)
@@ -42,5 +42,5 @@
 *  *Ellipsoid* - ellipsoidal shapes (oblate,prolate, core shell, etc)
 *  *Parellelepiped* - as the name implies
-*  *Sphere* - sheroidal shapes (sphere, core multishell, vesicle, etc)
+*  *Sphere* - spheroidal shapes (sphere, core multishell, vesicle, etc)
 *  *Lamellae* - lamellar shapes (lamellar, core shell lamellar, stacked
    lamellar, etc)
@@ -61,4 +61,37 @@
 on the *Description* button to the right.
 
+Product Models
+^^^^^^^^^^^^^^
+
+S(Q) models can be combined with many models in the other categories to
+generate what SasView calls "product models". The combination can be done by
+one of two methods, but how they behave is slightly different.
+
+The first, most straightforward, method is simply to use the S(Q) drop-down in
+the FitPage:
+
+.. figure:: p_and_s_buttons.png
+
+This example would then generate a product model with the following parameters:
+
+.. figure:: p_and_s_buttons_parameters.png
+
+The other method is to use the :ref:`Sum|Multi(p1,p2)` tool under Fitting >
+Plugin Model Operations:
+
+.. figure:: p_and_s_sum_model.png
+
+This creates a product model with the following parameters:
+
+.. figure:: p_and_s_sum_model_parameters.png
+
+As can be seen, the second method has produced a product model with an extra
+parameter: *radius_effective*. This is the radial distance determining the
+range of the $S(Q)$ interaction and may, or may not, be the same as the
+*radius*, in this example, depending on the concentration of the system. In
+other systems, *radius_effective* may depend on the particle form (shape).
+
+See :ref:`Product_Models` for more information.
+
 Show 1D/2D
 ^^^^^^^^^^
@@ -119,5 +152,5 @@
 
 For a complete list of all the library models available in SasView, see
-the `Model Documentation <../../../index.html>`_ .
+the `Model Documentation <../../../sasgui/perspectives/fitting/models/index.html>`_ .
 
 It is also possible to add your own models.
@@ -217,4 +250,6 @@
 a P(Q) model has been selected).
 
+.. _Sum|Multi(p1,p2):
+
 Sum|Multi(p1,p2)
 ^^^^^^^^^^^^^^^^
@@ -338,4 +373,36 @@
 These optimisers form the *Bumps* package written by P Kienzle. For more information
 on each optimiser, see the :ref:`Fitting_Documentation`.
+
+.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
+
+Fitting Integer Parameters
+--------------------------
+
+Most of the parameters in SasView models will naturally take floating point (decimal) 
+values, but there are some parameters which can only have integer values. Examples 
+include, but are not limited to, the number of shells in a multilayer vesicle, the 
+number of beads in a pearl necklace, the number of arms of a star polymer, and so on.
+Wherever possible/recognised, the integer nature of a parameter is specified in the 
+respective model documentation and/or parameter table, so read the documentation 
+carefully!
+
+Integer parameters must be fitted with care.
+
+Start with your best possible guess for the value of the parameter. And using 
+*a priori* knowledge, fix as many of the other parameters as possible.
+ 
+The SasView optimizers treat integer parameters internally as floating point 
+numbers, but the values presented to the user are truncated or rounded, as 
+appropriate.
+
+In most instances integer parameters will probably be greater than zero. A good 
+policy in such cases is to use a constraint to enforce this.
+
+Because an integer parameter should, by definition, only move in integer steps, 
+problems may be encountered if the optimizer step size is too small. Similarly, 
+be **very careful** about applying polydispersity to integer parameters.
+
+The Levenberg-Marquardt and Quasi-Newton BFGS (and other derivative-based) 
+optimizers are probably best avoided for fitting models with integer parameters.
 
 .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
