diff --git a/solutions/object_oriented_design/call_center/call_center.ipynb b/solutions/object_oriented_design/call_center/call_center.ipynb
index c540c6a6..8978e19c 100644
--- a/solutions/object_oriented_design/call_center/call_center.ipynb
+++ b/solutions/object_oriented_design/call_center/call_center.ipynb
@@ -106,28 +106,28 @@
     "\n",
     "class Operator(Employee):\n",
     "\n",
-    "    def __init__(self, employee_id, name):\n",
-    "        super(Operator, self).__init__(employee_id, name, Rank.OPERATOR)\n",
+    "    def __init__(self, employee_id, name, call_center):\n",
+    "        super(Operator, self).__init__(employee_id, name, Rank.OPERATOR, call_center)\n",
     "\n",
     "    def escalate_call(self):\n",
-    "        self.call.level = Rank.SUPERVISOR\n",
+    "        self.call.rank = Rank.SUPERVISOR\n",
     "        self._escalate_call()\n",
     "\n",
     "\n",
     "class Supervisor(Employee):\n",
     "\n",
-    "    def __init__(self, employee_id, name):\n",
-    "        super(Operator, self).__init__(employee_id, name, Rank.SUPERVISOR)\n",
+    "    def __init__(self, employee_id, name, call_center):\n",
+    "        super(Operator, self).__init__(employee_id, name, Rank.SUPERVISOR, call_center)\n",
     "\n",
     "    def escalate_call(self):\n",
-    "        self.call.level = Rank.DIRECTOR\n",
+    "        self.call.rank = Rank.DIRECTOR\n",
     "        self._escalate_call()\n",
     "\n",
     "\n",
     "class Director(Employee):\n",
     "\n",
-    "    def __init__(self, employee_id, name):\n",
-    "        super(Operator, self).__init__(employee_id, name, Rank.DIRECTOR)\n",
+    "    def __init__(self, employee_id, name, call_center):\n",
+    "        super(Operator, self).__init__(employee_id, name, Rank.DIRECTOR, call_center)\n",
     "\n",
     "    def escalate_call(self):\n",
     "        raise NotImplemented('Directors must be able to handle any call')\n",
diff --git a/solutions/object_oriented_design/call_center/call_center.py b/solutions/object_oriented_design/call_center/call_center.py
index 1d5e7bc6..54d42298 100644
--- a/solutions/object_oriented_design/call_center/call_center.py
+++ b/solutions/object_oriented_design/call_center/call_center.py
@@ -42,28 +42,28 @@ class Employee(metaclass=ABCMeta):
 
 class Operator(Employee):
 
-    def __init__(self, employee_id, name):
-        super(Operator, self).__init__(employee_id, name, Rank.OPERATOR)
+    def __init__(self, employee_id, name, call_center):
+        super(Operator, self).__init__(employee_id, name, Rank.OPERATOR, call_center)
 
     def escalate_call(self):
-        self.call.level = Rank.SUPERVISOR
+        self.call.rank = Rank.SUPERVISOR
         self._escalate_call()
 
 
 class Supervisor(Employee):
 
-    def __init__(self, employee_id, name):
-        super(Operator, self).__init__(employee_id, name, Rank.SUPERVISOR)
+    def __init__(self, employee_id, name, call_center):
+        super(Operator, self).__init__(employee_id, name, Rank.SUPERVISOR, call_center)
 
     def escalate_call(self):
-        self.call.level = Rank.DIRECTOR
+        self.call.rank = Rank.DIRECTOR
         self._escalate_call()
 
 
 class Director(Employee):
 
-    def __init__(self, employee_id, name):
-        super(Operator, self).__init__(employee_id, name, Rank.DIRECTOR)
+    def __init__(self, employee_id, name, call_center):
+        super(Operator, self).__init__(employee_id, name, Rank.DIRECTOR, call_center)
 
     def escalate_call(self):
         raise NotImplementedError('Directors must be able to handle any call')