Index: sasmodels/models/stickyhardsphere.py
===================================================================
--- sasmodels/models/stickyhardsphere.py	(revision 0507e09b26f5789862db8a175d64657cf4f3b829)
+++ sasmodels/models/stickyhardsphere.py	(revision db1d9d5f306f6645d007300bc421fb71d3669eda)
@@ -1,23 +1,23 @@
 # Note: model title and parameter table are inserted automatically
 r"""
-This calculates the interparticle structure factor for a hard sphere fluid
-with a narrow attractive well. A perturbative solution of the Percus-Yevick
-closure is used. The strength of the attractive well is described in terms
-of "stickiness" as defined below.
-
-The perturb (perturbation parameter), $\epsilon$, should be held between 0.01
-and 0.1. It is best to hold the perturbation parameter fixed and let
-the "stickiness" vary to adjust the interaction strength. The stickiness,
-$\tau$, is defined in the equation below and is a function of both the
-perturbation parameter and the interaction strength. $\tau$ and $\epsilon$
-are defined in terms of the hard sphere diameter $(\sigma = 2 R)$, the
-width of the square well, $\Delta$ (same units as $R$\ ), and the depth of
-the well, $U_o$, in units of $kT$. From the definition, it is clear that
-smaller $\tau$ means stronger attraction.
+Calculates the interparticle structure factor for a hard sphere fluid
+with a narrow, attractive, potential well. Unlike the :ref:`squarewell`
+model, here a perturbative solution of the Percus-Yevick closure
+relationship is used. The strength of the attractive well is described
+in terms of "stickiness" as defined below.
+
+The perturbation parameter (perturb), $\tau$, should be fixed between 0.01
+and 0.1 and the "stickiness", $\epsilon$, allowed to vary to adjust the
+interaction strength. The "stickiness" is defined in the equation below and is
+a function of both the perturbation parameter and the interaction strength.
+$\epsilon$ and $\tau$ are defined in terms of the hard sphere diameter $(\sigma = 2 R)$,
+the width of the square well, $\Delta$ (having the same units as $R$\ ),
+and the depth of the well, $U_o$, in units of $kT$. From the definition, it
+is clear that smaller $\epsilon$ means a stronger attraction.
 
 .. math::
 
-    \tau     &= \frac{1}{12\epsilon} \exp(u_o / kT) \\
-    \epsilon &= \Delta / (\sigma + \Delta)
+    \epsilon     &= \frac{1}{12\tau} \exp(u_o / kT) \\
+    \tau &= \Delta / (\sigma + \Delta)
 
 where the interaction potential is
@@ -31,23 +31,32 @@
         \end{cases}
 
-The Percus-Yevick (PY) closure was used for this calculation, and is an
-adequate closure for an attractive interparticle potential. This solution
+The Percus-Yevick (PY) closure is used for this calculation, and is an
+adequate closure for an attractive interparticle potential. The solution
 has been compared to Monte Carlo simulations for a square well fluid, with
 good agreement.
 
-The true particle volume fraction, $\phi$, is not equal to $h$, which appears
-in most of the reference. The two are related in equation (24) of the
-reference. The reference also describes the relationship between this
-perturbation solution and the original sticky hard sphere (or adhesive
-sphere) model by Baxter.
-
-**NB**: The calculation can go haywire for certain combinations of the input
-parameters, producing unphysical solutions - in this case errors are
-reported to the command window and the $S(q)$ is set to -1 (so it will
-disappear on a log-log plot). Use tight bounds to keep the parameters to
-values that you know are physical (test them) and keep nudging them until
-the optimization does not hit the constraints.
-
-In sasview the effective radius may be calculated from the parameters
+The true particle volume fraction, $\phi$, is not equal to $h$ which appears
+in most of reference [1]. The two are related in equation (24). Reference
+[1] also describes the relationship between this perturbative solution and
+the original sticky hard sphere (or "adhesive sphere") model of Baxter [2].
+
+.. note::
+
+   The calculation can go haywire for certain combinations of the input
+   parameters, producing unphysical solutions. In this case errors are
+   reported to the command window and $S(q)$ is set to -1 (so it will
+   disappear on a log-log plot!).
+
+   Use tight bounds to keep the parameters to values that you know are
+   physical (test them), and keep nudging them until the optimization
+   does not hit the constraints.
+
+.. note::
+
+   Earlier versions of SasView did not incorporate the so-called
+   $\beta(q)$ ("beta") correction [3] for polydispersity and non-sphericity.
+   This is only available in SasView versions 4.2.2 and higher.
+
+In SasView the effective radius may be calculated from the parameters
 used in the form factor $P(q)$ that this $S(q)$ is combined with.
 
@@ -65,4 +74,8 @@
 .. [#] S V G Menon, C Manohar, and K S Rao, *J. Chem. Phys.*, 95(12) (1991) 9186-9190
 
+.. [#] R J Baxter, *J. Chem. Phys.*, 49 (1968), 2770-2774
+
+.. [#] M Kotlarchyk and S-H Chen, *J. Chem. Phys.*, 79 (1983) 2461-2469
+
 Source
 ------
@@ -73,7 +86,7 @@
 ----------------------------
 
-* **Author:** 
-* **Last Modified by:** 
-* **Last Reviewed by:** 
+* **Author:**
+* **Last Modified by:**
+* **Last Reviewed by:** Steve King **Date:** March 27, 2019
 * **Source added by :** Steve King **Date:** March 25, 2019
 """
@@ -85,12 +98,12 @@
 
 name = "stickyhardsphere"
-title = "Sticky hard sphere structure factor, with Percus-Yevick closure"
+title = "'Sticky' hard sphere structure factor with Percus-Yevick closure"
 description = """\
     [Sticky hard sphere structure factor, with Percus-Yevick closure]
-        Interparticle structure factor S(Q)for a hard sphere fluid with
-        a narrow attractive well. Fits are prone to deliver non-physical
-        parameters, use with care and read the references in the full manual.
-        In sasview the effective radius will be calculated from the
-        parameters used in P(Q).
+        Interparticle structure factor S(Q) for a hard sphere fluid
+    with a narrow attractive well. Fits are prone to deliver non-
+    physical parameters; use with care and read the references in
+    the model documentation.The "beta(q)" correction is available
+    in versions 4.2.2 and higher.
 """
 category = "structure-factor"
@@ -107,7 +120,7 @@
      "volume fraction of hard spheres"],
     ["perturb", "", 0.05, [0.01, 0.1], "",
-     "perturbation parameter, epsilon"],
+     "perturbation parameter, tau"],
     ["stickiness", "", 0.20, [-inf, inf], "",
-     "stickiness, tau"],
+     "stickiness, epsilon"],
     ]
 
