diff --git a/product/ERP5/interfaces/transformation.py b/product/ERP5/interfaces/transformation.py
index dbf80c447cfedb433124f0d92a81c062f2ca298a..9c8fe0d7c111ff0f79998a492a9e8763de7b9b3d 100644
--- a/product/ERP5/interfaces/transformation.py
+++ b/product/ERP5/interfaces/transformation.py
@@ -6,10 +6,10 @@
 #                    Łukasz Nowak <luke@nexedi.com>
 #
 # WARNING: This program as such is intended to be used by professional
-# programmers who take the whole responsability of assessing all potential
+# programmers who take the whole responsibility of assessing all potential
 # consequences resulting from its eventual inadequacies and bugs
 # End users who are looking for a ready-to-use solution with commercial
-# garantees and support are strongly adviced to contract a Free Software
+# guarantees and support are strongly advised to contract a Free Software
 # Service Company
 #
 # This program is Free Software; you can redistribute it and/or
@@ -28,26 +28,23 @@
 #
 ##############################################################################
 
-# simple interface which have to be implemented on TradeModelLine,
-# Transformation, Pay Sheet Model, etc
 from zope.interface import Interface
 
 class ITransformation(Interface):
   """
     Common Interface to implementing querying of Indirect Amount
-    Models (TaxModelLine, InvoiceModelLine) shall be based on this interface
-
-    TODO:
-      - define parameters precisely for each method
+    Models (TaxModelLine, InvoiceModelLine, etc) shall be based on this
+    interface
   """
 
   def getAggregatedAmountList(context, movement_list=None, rounding=False):
-    """Returns implementation specific AggregatedAmountList of amounts
-    generated by set of rules
+    """Returns list of amounts generated by set of models
 
     context - represents object for which calculation shall happen
+
     movement_list - optional argument, movement list to apply on, if not passed
       it will be generated from passed context
+
     rounding - boolean argument, which controls if rounding shall be applied on
       generated movements or not
 
@@ -61,16 +58,19 @@ class ITransformation(Interface):
     pass
 
   def updateAggregatedAmountList(context, movement_list=None, rounding=False):
-    """Updates existing movement and returns new or deleted if any.
-
-    Returns a dictionary of list of movement 'movement_to_add_list' and
-    'movement_to_delete_list'
+    """Updates existing movement and returns new or deleted if any according to model
 
     context - represents object on which update shall happen
+
     movement_list - optional argument, movement list to apply on, if not passed
       it will be generated from passed context
+
     rounding - boolean argument, which controls if rounding shall be applied on
       generated movements or not
+
+    Returns a dictionary of list of instances of AggregatedAmountList class.
+    Dictionary contain lists described by keys:
+      * movement_to_add_list - list for movements which shall be added
+      * movement_to_delete_list - list of movements which shall be deleted
     """
     pass
-