diff --git a/CHANGELOG b/CHANGELOG
index d2a9d15b1d..c278ed60fb 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,4 @@
+* Add constant interpolation on line graph
 * Add create/delete field access
 * Add dynamic size limit on the One2Many, Many2Many and Char
 * Replace __tryton__.py by tryton.cfg
diff --git a/doc/topics/views/index.rst b/doc/topics/views/index.rst
index 06b0dae04c..2d42f7e28c 100644
--- a/doc/topics/views/index.rst
+++ b/doc/topics/views/index.rst
@@ -541,6 +541,22 @@ field
     * ``empty``: defined if the line graph must put a point for missing
       dates.
 
+    * ``interpolation``: defined how the line graph must interpolate points.
+      The default is ``linear``.
+
+        * ``constant-center``: use the value of the nearest point, see
+          `Nearest-neighbor interpolation`_
+
+        * ``constant-left``: use the value of the nearest left point.
+
+        * ``constant-right``: use the value of the nearest right point.
+
+        * ``linear``: see `linear interpolation`_
+
+.. _`Nearest-neighbor interpolation`:
+    http://en.wikipedia.org/wiki/Nearest-neighbor_interpolation
+.. _`linear interpolation`: http://en.wikipedia.org/wiki/Linear_interpolation
+
 
 Example
 -------
diff --git a/trytond/ir/ui/graph.rnc b/trytond/ir/ui/graph.rnc
index 2d19297a78..3a74cfc563 100644
--- a/trytond/ir/ui/graph.rnc
+++ b/trytond/ir/ui/graph.rnc
@@ -25,6 +25,9 @@ attlist.field &= attribute empty { "0" | "1" }?
 attlist.field &= attribute color { text }?
 attlist.field &= attribute widget { "float_time" }?
 attlist.field &= attribute float_time { text }?
+attlist.field &=
+    [ a:defaultValue = "linear" ]
+    attribute interpolation { "constant-left" | "constant-right" | "constant-center" | "linear" }?
 data = element data { attlist.data, xpath+ }
 attlist.data &= empty
 xpath = element xpath { attlist.xpath,
diff --git a/trytond/ir/ui/graph.rng b/trytond/ir/ui/graph.rng
index 71cdb68961..125c49c339 100644
--- a/trytond/ir/ui/graph.rng
+++ b/trytond/ir/ui/graph.rng
@@ -125,6 +125,18 @@
       <attribute name="float_time"/>
     </optional>
   </define>
+  <define name="attlist.field" combine="interleave">
+    <optional>
+      <attribute name="interpolation" a:defaultValue="linear">
+        <choice>
+          <value>constant-left</value>
+          <value>constant-right</value>
+          <value>constant-center</value>
+          <value>linear</value>
+        </choice>
+      </attribute>
+    </optional>
+  </define>
   <define name="data">
     <element name="data">
       <ref name="attlist.data"/>