diff --git a/docs/source/experiment.rst b/docs/source/experiment.rst
index 875322c..0df499f 100644
--- a/docs/source/experiment.rst
+++ b/docs/source/experiment.rst
@@ -462,28 +462,31 @@ beamline regularly updates a particular detector's mask as bad pixels are identi
              overwrite the existing mask. It is important therefore that
              the external pixel mask also excludes the detector gaps.
 
-After launching the dialog, the current mask can be plotted by clicking
-on "Plot Mask." This overlays the mask on the powder diffraction data to
-enable the center of the beam and other features of the data to be
-identified. 
+After launching the dialog, the current mask is automatically plotted,
+as an overlay on the powder diffraction data to enable the center of the
+beam and other features of the data to be identified. 
 
 .. figure:: /images/create-mask.png
    :align: center
    :width: 80%
 
-   *Create Mask dialog. The translucent red circle shows the circle
+   *Create Mask dialog. The translucent shape shows the rectangle
    created by clicking "Add Shape".*
 
 By clicking on "Add Shape" with either a rectangle or circle selected, a
 translucent shape is added to the plot. By default, it is centered on
 the beam center, but may be moved by dragging the center of the shape
 and/or resized by dragging one of the shape edges. When the shape has
-the correct position and size, click on "Add Shape" again for the shape
-to be added to the current list. A pull-down menu allows existing shapes
-to be selected for removal if necessary.
+the correct position and size, click on "Save Shape" for the shape to be
+added to the current list. After saving the shape, it is no longer
+draggable. However, the shape can still be modified by adjusting the
+shape parameters and then clicking on "Save Shape" again. A pull-down
+menu allows existing shapes to be selected for further edits or removal
+if necessary.
 
 If a more complicated mask is required, it can be generated by an
 external image editor and imported using "Import Mask".
 
-When the mask is complete, click "Save" to save it to the configuration file.
+When the mask is complete, click "Save" to save it to the configuration
+file.
 
diff --git a/docs/source/images/create-mask.png b/docs/source/images/create-mask.png
index 427c4f7..dd1ba73 100644
Binary files a/docs/source/images/create-mask.png and b/docs/source/images/create-mask.png differ