diff --git a/glances/attribute.py b/glances/attribute.py
index 0f96bb0f..7cfb65a4 100644
--- a/glances/attribute.py
+++ b/glances/attribute.py
@@ -2,7 +2,7 @@
 #
 # This file is part of Glances.
 #
-# Copyright (C) 2015 Nicolargo <nicolas@nicolargo.com>
+# Copyright (C) 2016 Nicolargo <nicolas@nicolargo.com>
 #
 # Glances is free software; you can redistribute it and/or modify
 # it under the terms of the GNU Lesser General Public License as published by
@@ -19,24 +19,24 @@
 
 """Attribute class."""
 
-from time import time
+from datetime import datetime
 
 
 class GlancesAttribute(object):
 
-    def __init__(self, name, description='', history_max_size=None, is_rate=False):
+    def __init__(self, name, description='', history_max_size=None):
         """Init the attribute
         name: Attribute name (string)
         description: Attribute human reading description (string)
         history_max_size: Maximum size of the history list (default is no limit)
-        is_rate: If True then the value is manage like a rate (store timestamp in the history)
+
+        History is stored as a list for tuple: [(date, value), ...]
         """
         self._name = name
         self._description = description
         self._value = None
         self._history_max_size = history_max_size
         self._history = []
-        self.is_rate = is_rate
 
     def __repr__(self):
         return self.value
@@ -71,25 +71,18 @@ class GlancesAttribute(object):
     """
     @property
     def value(self):
-        if self.is_rate:
-            if self.history_len() > 0:
-                return (self._value[1] - self.history_value()[1]) / (self._value[0] - self.history_value()[0])
-            else:
-                return None
+        if self.history_len() > 0:
+            return (self._value[1] - self.history_value()[1]) / (self._value[0] - self.history_value()[0])
         else:
-            return self._value
+            return None
 
     @value.setter
     def value(self, new_value):
         """Set a value.
-        If self.is_rate is True, store a tuple with (<timestamp>, value)
-        else, store directly the value (wathever type is it)
+        Value is a tuple: (<timestamp>, <new_value>)
         """
-        if self.is_rate:
-            new_value = (time(), new_value)
-        if self._value is not None:
-            self.history_add(self._value)
-        self._value = new_value
+        self._value = (datetime.now(), new_value)
+        self.history_add(self._value)
 
     """
     Properties for the attribute history
@@ -136,8 +129,5 @@ class GlancesAttribute(object):
     def history_mean(self, nb=5):
         """Return the mean on the <nb> values in the history.
         """
-        if self.is_rate:
-            h_sum = map(sum, zip(*self._history[-nb:]))
-            return h_sum[1] / float(self._history[-1][0] - self._history[-nb][0])
-        else:
-            return sum(self._history[-nb:]) / float(nb)
+        h_sum = map(sum, zip(*self._history[-nb:]))
+        return h_sum[1] / float(self._history[-1][0] - self._history[-nb][0])
diff --git a/glances/exports/graph.py b/glances/exports/graph.py
index 39c5f324..4d6f7a61 100644
--- a/glances/exports/graph.py
+++ b/glances/exports/graph.py
@@ -121,7 +121,9 @@ class GlancesGraph(object):
                     plt.ylabel(self.get_graph_yunit(i, pre_label=''))
                     # Curves
                     plt.grid(True)
-                    plt.plot_date(h['date'], h[i['name']],
+                    # Points are stored as tuple (date, value)
+                    x, y = zip(*h[i['name']])
+                    plt.plot_date(x, y,
                                   fmt='', drawstyle='default', linestyle='-',
                                   color=self.get_graph_color(i),
                                   xdate=True, ydate=False)
@@ -145,9 +147,13 @@ class GlancesGraph(object):
                             index_item += 1
                             plt.subplot(
                                 len(stats_history_filtered), 1, index_item)
+                            # Legend
                             plt.ylabel(self.get_graph_yunit(i, pre_label=k))
+                            # Curves
                             plt.grid(True)
-                            plt.plot_date(h['date'], h[k],
+                            # Points are stored as tuple (date, value)
+                            x, y = zip(*h[k])
+                            plt.plot_date(x, y,
                                           fmt='', drawstyle='default', linestyle='-',
                                           color=self.get_graph_color(i),
                                           xdate=True, ydate=False)
diff --git a/glances/history.py b/glances/history.py
index 027ce755..6e75d6cb 100644
--- a/glances/history.py
+++ b/glances/history.py
@@ -26,7 +26,7 @@ class GlancesHistory(object):
 
     """This class manage a dict of GlancesAttribute
     - key: stats name
-    - GlancesAttribute: history value"""
+    - value: GlancesAttribute"""
 
     def __init__(self):
         """
@@ -36,14 +36,12 @@ class GlancesHistory(object):
 
     def add(self, key, value,
             description='',
-            history_max_size=None,
-            is_rate=False):
+            history_max_size=None):
         """Add an new item (key, value) to the current history."""
         if key not in self.stats_history:
             self.stats_history[key] = GlancesAttribute(key,
                                                        description=description,
-                                                       history_max_size=history_max_size,
-                                                       is_rate=is_rate)
+                                                       history_max_size=history_max_size)
         self.stats_history[key].value = value
 
     def reset(self):
diff --git a/glances/plugins/glances_plugin.py b/glances/plugins/glances_plugin.py
index 6483ed9c..8b7df5f4 100644
--- a/glances/plugins/glances_plugin.py
+++ b/glances/plugins/glances_plugin.py
@@ -106,7 +106,7 @@ class GlancesPlugin(object):
         if (self.stats and self.args is not None and
                 self.args.export_graph and
                 self.get_items_history_list() is not None):
-            self.stats_history.add('date', datetime.now())
+            # self.stats_history.add('date', datetime.now())
             for i in self.get_items_history_list():
                 if isinstance(self.stats, list):
                     # Stats is a list of data