diff --git a/bin/fuzzycomparevtu.py b/bin/fuzzycomparevtu.py
index 194de61d9..8841be3d0 100755
--- a/bin/fuzzycomparevtu.py
+++ b/bin/fuzzycomparevtu.py
@@ -32,12 +32,14 @@ def isFuzzyEqual(vtkFile1, vtkFile2, absTol, relTol):
         for i in range(0, len(curVals1)):
             number1 = curVals1[i]
             number2 = curVals2[i]
-            if curFieldName.startswith("saturation") and abs(number1 - number2) > 1e-3:
-                print 'Difference between %f and %f too large in data field "%s: %s"'%(number1,number2,curFieldName,abs(number1 - number2))
-                return False
-            elif curFieldName.startswith("pressure") and abs(number1 - number2) > 0.1 and abs(number1 - number2) > 1e-5*abs(number1 + number2):
-                print 'Difference between %f and %f too large in data field "%s: %s"'%(number1,number2,curFieldName,abs(number1 - number2))
-                return False
+            if curFieldName.startswith("saturation"):
+                if abs(number1 - number2) > 1e-3:
+                    print 'Difference between %f and %f too large in data field "%s: %s"'%(number1,number2,curFieldName,abs(number1 - number2))
+                    return False
+            elif curFieldName.startswith("pressure"):
+                if abs(number1 - number2) > 0.1 and abs(number1 - number2) > 1e-5*abs(number1 + number2):
+                    print 'Difference between %f and %f too large in data field "%s: %s"'%(number1,number2,curFieldName,abs(number1 - number2))
+                    return False
             elif abs(number1 - number2) > absTol and number2 != 0 and abs(number1/number2 - 1) > relTol:
                 print 'Difference between %f and %f too large (%f%%) in data field "%s"'%(number1,number2,abs(number1/number2 - 1)*100, curFieldName)
                 return False
diff --git a/doc/handbook/fluidframework.tex b/doc/handbook/fluidframework.tex
index e0345b267..cc9e9cc4e 100644
--- a/doc/handbook/fluidframework.tex
+++ b/doc/handbook/fluidframework.tex
@@ -311,24 +311,17 @@ only needs to provide the following thermodynamic relations:
   phase.
   
   Molecular diffusion of a component $\kappa$ in phase $\alpha$ is
-  caused by a gradient of the chemical potential and follows the law
+  caused by a gradient of the chemical potential. Using some
+  simplifying assumptions~\cite{reid1987}, they can be also expressed
+  in terms of mole fraction gradients, i.e. the equation used for mass
+  fluxes due to molecular diffusion is
   \[ 
-  J^\kappa_\alpha = - D^\kappa_\alpha\ \mathbf{grad} \zeta^\kappa_\alpha\;,
+  J^\kappa_\alpha = - \rho_{mol,\alpha} D^\kappa_\alpha\ \mathbf{grad} x^\kappa_\alpha\;,
   \] 
-  where $\zeta^\kappa_\alpha$ is the component's chemical potential,
-  $D^\kappa_\alpha$ is the diffusion coefficient and $J^\kappa_\alpha$
-  is the diffusive flux. $\zeta^\kappa_\alpha$ is connected to the
-  component's fugacity $f^\kappa_\alpha$ by the relation
-  \[ 
-  \zeta^\kappa_\alpha = 
-  R T_\alpha \mathrm{ln} \frac{f^\kappa_\alpha}{p_\alpha} \;.
-  \]
-\item[binaryDiffusionCoefficient():] Given a fluid state, an
-  up-to-date parameter cache, a phase index and two component indices,
-  return the binary diffusion coefficient for the binary mixture. This
-  method is less general than \texttt{diffusionCoefficient} method,
-  but relations can only be found for binary diffusion coefficients in
-  the literature.
+  where $\rho_{mol,\alpha}$ is the molar density of phase $\alpha$,
+  $x^\kappa_\alpha$ is the mole fraction of component $\kappa$ in
+  phase $\alpha$, $D^\kappa_\alpha$ is the diffusion coefficient and
+  $J^\kappa_\alpha$ is the diffusive flux.
 \item[enthalpy():] Given a fluid state, an up-to-date parameter cache
   and a phase index, this method calulates the specific enthalpy
   $h_\alpha$ of the phase.