diff --git a/classes/science/border.py b/classes/science/border.py
index 39cf1fb..42bb767 100644
--- a/classes/science/border.py
+++ b/classes/science/border.py
@@ -1,4 +1,5 @@
 from classes.science.side import Side
+from gettext import gettext as _
 
 class Border:
     """
@@ -7,7 +8,7 @@ class Border:
 
     def __init__( self , x = Side() , y = Side() ):
         if not isinstance( x , Side ) or not isinstance( y , Side ):
-            raise ValueError( 'x and y should be sides' )
+            raise TypeError( _( 'x and y should be sides' ) )
         self.x = x
         self.y = y
 
diff --git a/classes/science/side.py b/classes/science/side.py
index c8fb3bf..21b64d3 100644
--- a/classes/science/side.py
+++ b/classes/science/side.py
@@ -1,3 +1,5 @@
+from gettext import gettext as _
+
 class Side:
     """
     Set of two index from the same axis
@@ -5,7 +7,7 @@ class Side:
 
     def __init__( self , min = 0 , max = 0 ):
         if not isinstance( min , int ) or not isinstance( max , int ):
-            raise ValueError( 'min and max should be int' )
+            raise TypeeError( _( 'min and max should be int' ) )
 
     def scale( self , factor ):
         """
@@ -13,6 +15,11 @@ class Side:
         """
         self.min = int( self.min * factor )
         self.max = int( self.max * factor )
+    def size( self ):
+        """
+        Compute size of the side
+        """
+        return self.max - self.min
     def __str__( self ):
         return '\
 side: [\