diff --git a/post/merge-scalar-data-arrays/README.md b/post/merge-scalar-data-arrays/README.md
new file mode 100644
index 0000000000000000000000000000000000000000..33513c1ea18b3d24f8b0e341a43ead097cc5f62a
--- /dev/null
+++ b/post/merge-scalar-data-arrays/README.md
@@ -0,0 +1,5 @@
+# Merge two scalar data arrays
+
+This script takes two scalar nodal fields from a vtu file and combines them to a
+two-component vector field.
+
diff --git a/post/mergeDataArrays.py b/post/merge-scalar-data-arrays/mergeDataArrays.py
similarity index 98%
rename from post/mergeDataArrays.py
rename to post/merge-scalar-data-arrays/mergeDataArrays.py
index ef87ec330da26778eb1b2dd200020b2cc5eb5cb2..58aea7caaab20ef70fd3a0ca77bee94590cdf33e 100755
--- a/post/mergeDataArrays.py
+++ b/post/merge-scalar-data-arrays/mergeDataArrays.py
@@ -11,7 +11,7 @@
 from vtk import *
 from sys import argv, exit
 
-if len(argv) < 6:
+if len(argv) != 6:
     print "Usage:", argv[0], "input.vtu scalar1 scalar2 vector_2d output.vtu"
     exit(1)