diff --git a/PowerDiagram.py b/PowerDiagram.py
index 6deca1b..9b19253 100644
--- a/PowerDiagram.py
+++ b/PowerDiagram.py
@@ -7,8 +7,8 @@
 '''
 
 import re
-import pygraphviz
-from inventory import Inventory
+import pygraphviz  # port install py-pygraphviz
+from inventory import Inventory, MachineSpecIdNotFound
 from SimpaDbUtil import SqlFile, SqlDatabaseReader
 from Lib import SimpaDbUtil
 
@@ -199,7 +199,9 @@ class PowerConfig(object):
 
             machine_name = machine.name
 
-            if re.match('simpatix.._..', machine_name):
+            if re.match('[a-z]+.._..', machine_name):
+                # machine_name is a group of machines such as physix80_83
+                # in this case, we use a hack : the type and power consumption is based on the first machine of this group (in this example physix80)
                 machine_name = '_'.join(machine_name.split('_')[0:-1])
 
             # print(machine_name)
@@ -210,7 +212,7 @@ class PowerConfig(object):
                 machine_spec_id = inventory.machine_name_to_machine_spec_id(machine_name)
                 if machine_spec_id == '':
                     machine_spec_id = None  # some simple 'machines' such as powerext003 have undefined machine_spec_id
-            except SimpaDbUtil.TableAttrNotFound:
+            except MachineSpecIdNotFound:
                 pass
                         
             if machine_spec_id is not None:
diff --git a/SimpaDbUtil.py b/SimpaDbUtil.py
index 118f1bc..98b7736 100644
--- a/SimpaDbUtil.py
+++ b/SimpaDbUtil.py
@@ -1,4 +1,4 @@
-import MySQLdb
+import MySQLdb  # sudo port install py-mysql
 import time
 import StringIO
 import re
diff --git a/inventory.py b/inventory.py
index c0fc408..0c96e5a 100644
--- a/inventory.py
+++ b/inventory.py
@@ -45,7 +45,10 @@ class Inventory(object):
         return machine_name
 
     def machine_name_to_machine_spec_id(self, machine_name):
-        machine_spec_id = self._sql_reader.get_table_attr('machines', 'name', machine_name, 'machine_spec_id')
+        try:
+            machine_spec_id = self._sql_reader.get_table_attr('machines', 'name', machine_name, 'machine_spec_id')
+        except SimpaDbUtil.TableAttrNotFound as e:  # @UnusedVariable
+            raise MachineSpecIdNotFound(machine_name)
         return machine_spec_id
 
     # electricity related methods