diff --git a/doc/src/fix_neb.rst b/doc/src/fix_neb.rst
index 4d0d301540..1d4c28f12b 100644
--- a/doc/src/fix_neb.rst
+++ b/doc/src/fix_neb.rst
@@ -120,14 +120,17 @@ and :math:`RD_{ideal}` is the ideal *RD* for which all the images are
 equally spaced.  I.e. :math:`RD_{ideal} = (i-1) \cdot meanDist` when the
 climbing replica is off, where *i* is the replica number).  The
 *meanDist* is the average distance between replicas.  Note that in this
-case the specified *Kspring* is in force units.
-
-Note that the *ideal* form of nudging can often be more effective at
-keeping the replicas equally spaced.
+case the specified *Kspring* is in force units. When the climbing replica 
+is on, :math:`RD_{ideal}` and :math:`meanDist` are calculated separately
+each side of the climbing image. Note that the *ideal* form of nudging 
+can often be more effective at keeping the replicas equally spaced before
+climbing, then equally spaced either side of the climbing image whilst 
+climbing. 
 
 With a value of *equal* the spring force is computed as for *ideal*
-before the climbing stage, then is computed to promote equidistant
-spacing in energy rather than distance:
+before the climbing stage, then during the climbing stage is modified 
+to promote equidistant absolute differnces in energy, rather than 
+distance, each side of the climbing image:
 
 .. math::
 
@@ -137,12 +140,16 @@ where *ED* is the cumulative sum of absolute energy differences:
 
 .. math::
 
-   ED = \sum_{i<N} \left|E(R_{i+1}) - E(R_i)\right|, \qquad ED_{ideal} = (N-1) \cdot meanEdist
+   ED = \sum_{i<N} \left|E(R_{i+1}) - E(R_i)\right|, 
 
-and *meanEdist* is the average absolute energy difference between
-replicas.  This form of nudging is to aid schemes which integrate forces
-along NEB pathways such as :doc:`fix_pafi <fix_pafi>`, by providing
-optimal quadrature points.
+*meanEdist* is the average absolute energy difference between
+replicas up to the climbing image or from the climbing image 
+to the final image, for images before or after the climbing 
+image respectively. :math:`ED_{ideal}` is the corresponding 
+cumulative sum of average absolute energy differences in 
+each case, just as for *ideal*. This form of nudging is 
+to aid schemes which integrate forces along, or near to, 
+NEB pathways such as :doc:`fix_pafi <fix_pafi>`.
 
 ----------