diff --git a/Code/Mantid/docs/source/algorithms/ReflectometryReductionOneAuto-v1.rst b/Code/Mantid/docs/source/algorithms/ReflectometryReductionOneAuto-v1.rst
index 2b1da4c473759426bb4199c50c245821df8e4276..933d2435362ab9c282b20bca38ef08ff39bfbd73 100644
--- a/Code/Mantid/docs/source/algorithms/ReflectometryReductionOneAuto-v1.rst
+++ b/Code/Mantid/docs/source/algorithms/ReflectometryReductionOneAuto-v1.rst
@@ -11,7 +11,13 @@ Description
 
 Facade over :ref:`algm-ReflectometryReductionOne`.
 
-Pulls numeric parameters out of the instrument parameters where possible. You can override any of these automatically applied defaultsby providing your own value for the input.
+Pulls numeric parameters out of the instrument parameters where possible. You can override any of these automatically applied defaults by providing your own value for the input.
+
+If ProcessingInstructions is not set its value is inferred from other properties:
+
+* If AnalysisMode = PointDetectorAnalaysis and PointDetectorStart = PointDetectorStop then the spectrum specified by PointDetectorStart is used.
+* If AnalysisMode = PointDetectorAnalaysis and PointDetectorStart ≠ PointDetectorStop then the sum of the spectra from PointDetectorStart to PointDetectorStop is used.
+* If AnalysisMode = MultiDetectorAnalaysis then all of the spectra from MultiDetectorStart onwards are used.
 
 See :ref:`algm-ReflectometryReductionOne` for more information on the wrapped algorithm.