diff --git a/resource_multi_week_calendar/__manifest__.py b/resource_multi_week_calendar/__manifest__.py
index f1f018a28a9..0b3a4368d21 100644
--- a/resource_multi_week_calendar/__manifest__.py
+++ b/resource_multi_week_calendar/__manifest__.py
@@ -6,7 +6,7 @@
     "name": "Multi-week calendars",
     "summary": """
         Allow a calendar to alternate between multiple weeks.""",
-    "version": "16.0.1.0.0",
+    "version": "12.0.1.0.0",
     "category": "Hidden",
     "website": "https://github.com/OCA/hr",
     "author": "Coop IT Easy SC, Odoo Community Association (OCA)",
diff --git a/resource_multi_week_calendar/models/resource_calendar.py b/resource_multi_week_calendar/models/resource_calendar.py
index 9aa530decd6..640310fe552 100644
--- a/resource_multi_week_calendar/models/resource_calendar.py
+++ b/resource_multi_week_calendar/models/resource_calendar.py
@@ -7,6 +7,7 @@
 
 from odoo import _, api, fields, models
 from odoo.exceptions import ValidationError
+from odoo.addons.resource.models.resource import Intervals
 
 
 class ResourceCalendar(models.Model):
@@ -221,44 +222,27 @@ def _split_into_weeks(self, start_dt, end_dt):
             # Move to the next week (start of next Monday)
             current_start = current_end
 
-    def _attendance_intervals_batch(
-        self, start_dt, end_dt, resources=None, domain=None, tz=None
-    ):
+    def _attendance_intervals(self, start_dt, end_dt, resource=None):
         self.ensure_one()
         if not self.is_multi_week:
-            return super()._attendance_intervals_batch(
-                start_dt, end_dt, resources=resources, domain=domain, tz=tz
-            )
+            return super()._attendance_intervals(start_dt, end_dt, resource=resource)
 
         calendars_by_week = {
             calendar.week_number: calendar for calendar in self.multi_week_calendar_ids
         }
-        results = []
+        result = Intervals()
 
         # Calculate each week separately, choosing the correct calendar for each
         # week.
         for week_start, week_end in self._split_into_weeks(start_dt, end_dt):
-            results.append(
-                super(
-                    ResourceCalendar,
-                    calendars_by_week[self._get_week_number(week_start)].with_context(
-                        # This context is not used here, but could possibly be
-                        # used by other modules that use this module. I am not
-                        # sure how useful it is.
-                        recursive_multi_week=True
-                    ),
-                )._attendance_intervals_batch(
-                    week_start, week_end, resources=resources, domain=domain, tz=tz
-                )
-            )
-
-        # Aggregate the results from each week.
-        result = {}
-        for item in results:
-            for resource, intervals in item.items():
-                if resource not in result:
-                    result[resource] = intervals
-                else:
-                    result[resource] |= intervals
+            result |= super(
+                ResourceCalendar,
+                calendars_by_week[self._get_week_number(week_start)].with_context(
+                    # This context is not used here, but could possibly be
+                    # used by other modules that use this module. I am not
+                    # sure how useful it is.
+                    recursive_multi_week=True
+                ),
+            )._attendance_intervals(week_start, week_end, resource=resource)
 
         return result
diff --git a/resource_multi_week_calendar/readme/ROADMAP.rst b/resource_multi_week_calendar/readme/ROADMAP.rst
index 158e0ee0555..31b06e98e14 100644
--- a/resource_multi_week_calendar/readme/ROADMAP.rst
+++ b/resource_multi_week_calendar/readme/ROADMAP.rst
@@ -2,9 +2,6 @@ This module is a template for building on top of. It _will_ need glue modules to
 work with various other modules. Most notably, ``hr_holidays`` will not work
 without modification.
 
-The existing base Odoo two-week calendar functionality is hidden rather than
-disabled. This may or may not be desirable.
-
 The module may need improvements for timezone handling; this is currently
 untested. ``_split_into_weeks`` splits weeks on the timezone of the datetime
 objects passed to it instead of on the timezone of the calendar. The calculation
diff --git a/resource_multi_week_calendar/tests/test_calendar.py b/resource_multi_week_calendar/tests/test_calendar.py
index 3f2fa12f69e..a1b89b54d1b 100644
--- a/resource_multi_week_calendar/tests/test_calendar.py
+++ b/resource_multi_week_calendar/tests/test_calendar.py
@@ -7,11 +7,10 @@
 from freezegun import freeze_time
 
 from odoo.exceptions import ValidationError
-from odoo.fields import Command
-from odoo.tests.common import TransactionCase
+from odoo.tests.common import SavepointCase
 
 
-class CalendarCase(TransactionCase):
+class CalendarCase(SavepointCase):
     @classmethod
     def setUpClass(cls):
         super().setUpClass()
@@ -56,15 +55,15 @@ def test_cant_add_parent_to_parent(self):
                 "week_sequence": 1,
             }
         )
+        parent_of_parent = self.Calendar.create(
+            {
+                "name": "Parent of parent",
+                # This value is kind of arbitrary here.
+                "week_sequence": 2,
+            }
+        )
         with self.assertRaises(ValidationError):
-            self.Calendar.create(
-                {
-                    "name": "Parent of parent",
-                    "child_calendar_ids": self.parent_calendar.ids,
-                    # This value is kind of arbitrary here.
-                    "week_sequence": 2,
-                }
-            )
+            parent_of_parent.child_calendar_ids = self.parent_calendar
 
 
 class TestCalendarIsMultiweek(CalendarCase):
@@ -220,50 +219,60 @@ def setUp(self):
         # In the child calendar, only work the mornings.
         self.child_2.attendance_ids = False
         self.child_2.attendance_ids = [
-            Command.create(
+            (
+                0,
+                False,
                 {
                     "name": "Monday Morning",
                     "dayofweek": "0",
                     "hour_from": 8,
                     "hour_to": 12,
                     "day_period": "morning",
-                }
+                },
             ),
-            Command.create(
+            (
+                0,
+                False,
                 {
                     "name": "Tuesday Morning",
                     "dayofweek": "1",
                     "hour_from": 8,
                     "hour_to": 12,
                     "day_period": "morning",
-                }
+                },
             ),
-            Command.create(
+            (
+                0,
+                False,
                 {
                     "name": "Wednesday Morning",
                     "dayofweek": "2",
                     "hour_from": 8,
                     "hour_to": 12,
                     "day_period": "morning",
-                }
+                },
             ),
-            Command.create(
+            (
+                0,
+                False,
                 {
                     "name": "Thursday Morning",
                     "dayofweek": "3",
                     "hour_from": 8,
                     "hour_to": 12,
                     "day_period": "morning",
-                }
+                },
             ),
-            Command.create(
+            (
+                0,
+                False,
                 {
                     "name": "Friday Morning",
                     "dayofweek": "4",
                     "hour_from": 8,
                     "hour_to": 12,
                     "day_period": "morning",
-                }
+                },
             ),
         ]
 
diff --git a/resource_multi_week_calendar/views/resource_calendar_views.xml b/resource_multi_week_calendar/views/resource_calendar_views.xml
index a51ca21d802..b927868b326 100644
--- a/resource_multi_week_calendar/views/resource_calendar_views.xml
+++ b/resource_multi_week_calendar/views/resource_calendar_views.xml
@@ -5,16 +5,12 @@
         <field name="model">resource.calendar</field>
         <field name="inherit_id" ref="resource.resource_calendar_form" />
         <field name="arch" type="xml">
-            <button name="switch_calendar_type" position="attributes">
-                <attribute name="attrs" />
-                <attribute name="invisible">1</attribute>
-            </button>
             <field name="hours_per_day" position="attributes">
                 <attribute
                     name="attrs"
                 >{'invisible': [('child_calendar_ids', '!=', [])]}</attribute>
             </field>
-            <group name="resource_details" position="inside">
+            <xpath expr="//field[@name='company_id']/.." position="after">
                 <group name="multi_week">
                     <!-- TODO: Should this be readonly? If it is, you cannot add
                          duplicated records to an existing relation. -->
@@ -49,8 +45,14 @@
                     <field name="current_week_number" />
                     <field name="current_multi_week_calendar_id" />
                 </group>
-            </group>
-            <xpath expr="//page[@name='working_hours']" position="attributes">
+            </xpath>
+            <!-- Hide the pages -->
+            <xpath expr="//field[@name='attendance_ids']/.." position="attributes">
+                <attribute name="attrs">
+                    {'invisible': [('child_calendar_ids', '!=', [])]}
+                </attribute>
+            </xpath>
+            <xpath expr="//field[@name='global_leave_ids']/.." position="attributes">
                 <attribute name="attrs">
                     {'invisible': [('child_calendar_ids', '!=', [])]}
                 </attribute>
@@ -63,7 +65,7 @@
         <field name="model">resource.calendar</field>
         <field name="inherit_id" ref="resource.view_resource_calendar_search" />
         <field name="arch" type="xml">
-            <xpath expr="//filter[@name='inactive']" position="before">
+            <xpath expr="//search" position="inside">
                 <filter
                     string="Only Main Working Times"
                     name="only_parent_calendars"