Merge pull request #1107 from g76r/f_diffseriesdoc

Fixed misleading doc for function diffSeries

webapp/graphite/render/functions.py

@@ -289,15 +289,24 @@ def multiplySeriesWithWildcards(requestContext, seriesList, *position): #XXX
 
 def diffSeries(requestContext, *seriesLists):
   """
-  Can take two or more metrics, or a single metric and a constant.
-  Subtracts parameters 2 through n from parameter 1.
+  Subtracts series 2 through n from series 1.
 
   Example:
 
   .. code-block:: none
 
     &target=diffSeries(service.connections.total,service.connections.failed)
-    &target=diffSeries(service.connections.total,5)
+
+  To diff a series and a constant, one should use offset instead of (or in
+  addition to) diffSeries
+
+  Example:
+
+  .. code-block:: none
+
+    &target=offset(service.connections.total,-5)
+
+    &target=offset(diffSeries(service.connections.total,service.connections.failed),-4)
 
   """
   (seriesList,start,end,step) = normalize(seriesLists)