diff --git a/doc/dev/database.rst b/doc/dev/database.rst
index c914b771..703c117a 100644
--- a/doc/dev/database.rst
+++ b/doc/dev/database.rst
@@ -534,12 +534,14 @@ they result in the "checked" time series.)
 
       The time series group to which this auto-process applies.
 
-   .. method:: execute()
-
-      Performs the auto-processing. It retrieves the new part of the
-      source time series (i.e. the part that starts after the last date
-      of the target time series) and calls the
-      :meth:`process_timeseries` method.
+   .. method:: execute(recalculate: bool)
+
+      Performs the auto-processing. If ``recalculate`` is ``False``, it
+      retrieves the new part of the source time series (i.e. the part that
+      starts after the last date of the target time series) and calls the
+      :meth:`process_timeseries` method. If ``recalculate`` is ``True``, it
+      deletes all records of the target timeseries first and therefore
+      recalculates its entirety.
 
    .. attribute:: source_timeseries
 
diff --git a/enhydris/autoprocess/apps.py b/enhydris/autoprocess/apps.py
index dba92c36..3afb4dba 100644
--- a/enhydris/autoprocess/apps.py
+++ b/enhydris/autoprocess/apps.py
@@ -6,13 +6,20 @@
 
 
 def enqueue_auto_process(sender, *, instance, **kwargs):
+    def enqueue_on_commit(auto_process_id: int, has_non_append_modifications: bool):
+        transaction.on_commit(
+            lambda: execute_auto_process.delay(
+                auto_process_id, has_non_append_modifications
+            )
+        )
+
     auto_processes = [
         auto_process
         for auto_process in instance.timeseries_group.autoprocess_set.all()
         if auto_process.as_specific_instance.source_timeseries == instance
     ]
     for auto_process in auto_processes:
-        transaction.on_commit(lambda: execute_auto_process.delay(auto_process.id))
+        enqueue_on_commit(auto_process.id, instance.has_non_append_modifications)
 
 
 class AutoprocessConfig(AppConfig):
diff --git a/enhydris/autoprocess/models.py b/enhydris/autoprocess/models.py
index e593f313..76a6bd70 100644
--- a/enhydris/autoprocess/models.py
+++ b/enhydris/autoprocess/models.py
@@ -6,6 +6,7 @@
 
 from django.db import DataError, IntegrityError, models, transaction
 from django.db.models.signals import post_delete
+from django.utils.functional import cached_property
 from django.utils.translation import gettext_lazy as _
 
 import numpy as np
@@ -27,10 +28,16 @@ class Meta:
         db_table = "enhydris_autoprocess_autoprocess"
         verbose_name_plural = _("Auto processes")
 
-    def execute(self):
+    def execute(self, recalculate: bool):
         try:
-            result = self.process_timeseries()
-            self.target_timeseries.insert_or_append_data(result)
+            with transaction.atomic():
+                target_timeseries = self.target_timeseries
+                if recalculate:
+                    target_timeseries.timeseriesrecord_set.all().delete()
+                    target_timeseries.has_non_append_modifications = True
+                    target_timeseries._invalidate_cached_data()
+                result = self.process_timeseries()
+                target_timeseries.insert_or_append_data(result)
         except Exception as e:
             msg = (
                 f"{e.__class__.__name__} while executing AutoProcess with "
@@ -74,14 +81,18 @@ def _get_start_date(self):
 
     def save(self, *args, **kwargs):
         result = super().save(*args, **kwargs)
-        transaction.on_commit(lambda: tasks.execute_auto_process.delay(self.id))
+        transaction.on_commit(
+            lambda: tasks.execute_auto_process.delay(
+                self.id, has_non_append_modifications=True
+            )
+        )
         return result
 
-    @property
+    @cached_property
     def source_timeseries(self):
         raise NotImplementedError("This property is available only in subclasses")
 
-    @property
+    @cached_property
     def target_timeseries(self):
         raise NotImplementedError("This property is available only in subclasses")
 
@@ -108,14 +119,14 @@ class Meta:
     def __str__(self):
         return _("Checks for {}").format(str(self.timeseries_group))
 
-    @property
+    @cached_property
     def source_timeseries(self):
         obj, created = self.timeseries_group.timeseries_set.get_or_create(
             type=Timeseries.INITIAL
         )
         return obj
 
-    @property
+    @cached_property
     def target_timeseries(self):
         obj, created = self.timeseries_group.timeseries_set.get_or_create(
             type=Timeseries.CHECKED,
@@ -319,7 +330,7 @@ class Meta:
     def __str__(self):
         return f"=> {self.target_timeseries_group}"
 
-    @property
+    @cached_property
     def source_timeseries(self):
         try:
             return self.timeseries_group.timeseries_set.get(type=Timeseries.CHECKED)
@@ -330,7 +341,7 @@ def source_timeseries(self):
         )
         return obj
 
-    @property
+    @cached_property
     def target_timeseries(self):
         obj, created = self.target_timeseries_group.timeseries_set.get_or_create(
             type=Timeseries.INITIAL
@@ -460,7 +471,7 @@ class Meta:
     def __str__(self):
         return _("Aggregation for {}").format(str(self.timeseries_group))
 
-    @property
+    @cached_property
     def source_timeseries(self):
         try:
             return self.timeseries_group.timeseries_set.get(type=Timeseries.CHECKED)
@@ -470,7 +481,7 @@ def source_timeseries(self):
             )
             return obj
 
-    @property
+    @cached_property
     def target_timeseries(self):
         obj, created = self.timeseries_group.timeseries_set.get_or_create(
             type=Timeseries.AGGREGATED,
diff --git a/enhydris/autoprocess/tasks.py b/enhydris/autoprocess/tasks.py
index 1d6e991e..91d3606f 100644
--- a/enhydris/autoprocess/tasks.py
+++ b/enhydris/autoprocess/tasks.py
@@ -2,7 +2,8 @@
 
 
 @app.task
-def execute_auto_process(auto_process_id):
+def execute_auto_process(auto_process_id, has_non_append_modifications: bool):
     from .models import AutoProcess
 
-    AutoProcess.objects.get(id=auto_process_id).as_specific_instance.execute()
+    auto_process = AutoProcess.objects.get(id=auto_process_id).as_specific_instance
+    auto_process.execute(recalculate=has_non_append_modifications)
diff --git a/enhydris/autoprocess/tests/test_apps.py b/enhydris/autoprocess/tests/test_apps.py
index 17c73eaf..5f4fb388 100644
--- a/enhydris/autoprocess/tests/test_apps.py
+++ b/enhydris/autoprocess/tests/test_apps.py
@@ -1,3 +1,4 @@
+from io import StringIO
 from unittest import mock
 
 from django.contrib.gis.geos import Point
@@ -38,10 +39,28 @@ def setUp(self, m1, m2):
     def test_enqueues_auto_process(self, m):
         with transaction.atomic():
             self.timeseries.save()
-        m.delay.assert_any_call(self.auto_process.id)
+        m.delay.assert_called_once_with(self.auto_process.id, False)
 
     @mock.patch("enhydris.autoprocess.apps.execute_auto_process")
     def test_auto_process_is_not_triggered_before_commit(self, m):
         with transaction.atomic():
             self.timeseries.save()
             m.delay.assert_not_called()
+
+    @mock.patch("enhydris.autoprocess.apps.execute_auto_process")
+    def test_inserting_data_enqueues_task_with_non_append_modifications_true(self, m):
+        self.timeseries.insert_or_append_data(
+            StringIO("2020-01-01 00:10,15,\n"),
+            default_timezone="UTC",
+            append_only=False,
+        )
+        m.delay.assert_called_once_with(self.auto_process.id, True)
+
+    @mock.patch("enhydris.autoprocess.apps.execute_auto_process")
+    def test_appending_data_enqueues_task_with_non_append_modifications_false(self, m):
+        self.timeseries.insert_or_append_data(
+            StringIO("2020-01-01 00:10,15,\n"),
+            default_timezone="UTC",
+            append_only=True,
+        )
+        m.delay.assert_called_once_with(self.auto_process.id, False)
diff --git a/enhydris/autoprocess/tests/test_models/test_aggregation.py b/enhydris/autoprocess/tests/test_models/test_aggregation.py
index a5fbd481..0fa675da 100644
--- a/enhydris/autoprocess/tests/test_models/test_aggregation.py
+++ b/enhydris/autoprocess/tests/test_models/test_aggregation.py
@@ -424,7 +424,7 @@ def setUp(self):
 
     def test_initial_target_timeseries(self):
         aggregation = Aggregation.objects.get(id=self.aggregation_id)
-        aggregation.execute()
+        aggregation.execute(recalculate=False)
         actual_data = aggregation.target_timeseries.get_data().data
         expected_data = pd.DataFrame(
             data={"value": [21.0, 34.0], "flags": ["", "MISSING2"]},
@@ -438,11 +438,11 @@ def test_initial_target_timeseries(self):
         pd.testing.assert_frame_equal(actual_data, expected_data)
 
     def test_updated_target_timeseries(self):
-        Aggregation.objects.get(id=self.aggregation_id).execute()
+        Aggregation.objects.get(id=self.aggregation_id).execute(recalculate=False)
 
         self._extend_source_timeseries()
         aggregation = Aggregation.objects.get(id=self.aggregation_id)
-        aggregation.execute()
+        aggregation.execute(recalculate=False)
 
         ahtimeseries = aggregation.target_timeseries.get_data()
         expected_data = pd.DataFrame(
@@ -514,13 +514,13 @@ def setUp(self):
 
     def test_result(self, m):
         aggregation = Aggregation.objects.get(id=self.aggregation_id)
-        aggregation.execute()
+        aggregation.execute(recalculate=False)
         actual_data = aggregation.target_timeseries.get_data().data
         self.assertEqual(len(actual_data), 0)
 
     def test_log(self, logging_mock):
         aggregation = Aggregation.objects.get(id=self.aggregation_id)
-        aggregation.execute()
+        aggregation.execute(recalculate=False)
         logging_mock.getLogger.return_value.error.assert_called_once_with(
             "Need at least 3 dates to infer frequency"
         )
diff --git a/enhydris/autoprocess/tests/test_models/test_autoprocess.py b/enhydris/autoprocess/tests/test_models/test_autoprocess.py
index e3c9c58a..15987bf2 100644
--- a/enhydris/autoprocess/tests/test_models/test_autoprocess.py
+++ b/enhydris/autoprocess/tests/test_models/test_autoprocess.py
@@ -62,7 +62,9 @@ def test_save_triggers_auto_process(self):
         with transaction.atomic():
             auto_process = baker.make(Checks, timeseries_group=self.timeseries_group)
             auto_process.save()
-        tasks.execute_auto_process.delay.assert_any_call(auto_process.id)
+        tasks.execute_auto_process.delay.assert_any_call(
+            auto_process.id, has_non_append_modifications=True
+        )
 
     def test_auto_process_is_not_triggered_before_commit(self):
         with transaction.atomic():
@@ -88,11 +90,11 @@ def setUp(self):
         self.range_check = baker.make(RangeCheck, checks=self.checks)
 
     def test_called_once(self, m):
-        self.checks.execute()
+        self.checks.execute(recalculate=False)
         self.assertEqual(len(m.mock_calls), 1)
 
     def test_called_with_empty_content(self, m):
-        self.checks.execute()
+        self.checks.execute(recalculate=False)
         self.assertEqual(len(self.checks.htimeseries.data), 0)
 
     def test_critical_error(self, m):
@@ -101,16 +103,16 @@ def test_critical_error(self, m):
             f"^ValueError while executing AutoProcess with id={self.checks.id}: hello$"
         )
         with self.assertRaisesRegex(RuntimeError, msg):
-            self.checks.execute()
+            self.checks.execute(recalculate=False)
 
 
-class AutoProcessExecuteDealsOnlyWithNewerTimeseriesPartTestCase(TestCase):
+class AutoProcessRecalculateTestCaseBase(TestCase):
     @mock.patch(
         "enhydris.autoprocess.models.Checks.process_timeseries",
         side_effect=lambda self: self.htimeseries,
         autospec=True,
     )
-    def setUp(self, m):
+    def setUp(self, m: mock.MagicMock):
         self.mock_process_timeseries = m
         station = baker.make(Station, display_timezone="Etc/GMT-2")
         self.timeseries_group = baker.make(
@@ -149,7 +151,11 @@ def setUp(self, m):
         )
         self.checks = baker.make(Checks, timeseries_group=self.timeseries_group)
         self.range_check = baker.make(RangeCheck, checks=self.checks)
-        self.checks.execute()
+        self.checks.execute(recalculate=self.recalculate)
+
+
+class AutoProcessExecuteRecalculateFalseTestCase(AutoProcessRecalculateTestCaseBase):
+    recalculate = False
 
     def test_called_once(self):
         self.assertEqual(len(self.mock_process_timeseries.mock_calls), 1)
@@ -181,3 +187,21 @@ def test_appended_the_data(self):
         pd.testing.assert_frame_equal(
             self.target_timeseries.get_data().data, expected_result
         )
+
+
+class AutoProcessExecuteRecalculateTestCase(AutoProcessRecalculateTestCaseBase):
+    recalculate = True
+
+    def test_called_with_entire_source_timeseries(self):
+        expected_arg = pd.DataFrame(
+            data={"value": [1.0, 2.0, 3.0, 4.0], "flags": ["", "", "", ""]},
+            columns=["value", "flags"],
+            index=[
+                dt.datetime(2019, 5, 21, 17, 0, tzinfo=get_tzinfo("Etc/GMT-2")),
+                dt.datetime(2019, 5, 21, 17, 10, tzinfo=get_tzinfo("Etc/GMT-2")),
+                dt.datetime(2019, 5, 21, 17, 20, tzinfo=get_tzinfo("Etc/GMT-2")),
+                dt.datetime(2019, 5, 21, 17, 30, tzinfo=get_tzinfo("Etc/GMT-2")),
+            ],
+        )
+        expected_arg.index.name = "date"
+        pd.testing.assert_frame_equal(self.checks.htimeseries.data, expected_arg)
diff --git a/enhydris/autoprocess/tests/test_models/test_checks.py b/enhydris/autoprocess/tests/test_models/test_checks.py
index db03e16d..60e332ab 100644
--- a/enhydris/autoprocess/tests/test_models/test_checks.py
+++ b/enhydris/autoprocess/tests/test_models/test_checks.py
@@ -97,7 +97,7 @@ def test_runs_range_check(self, m1, m2):
             checks__timeseries_group__gentity=station,
             checks__timeseries_group__variable__descr="Temperature",
         )
-        range_check.checks.execute()
+        range_check.checks.execute(recalculate=False)
         m2.assert_called_once()
 
     def test_no_extra_queries_for_str(self):
diff --git a/enhydris/autoprocess/tests/test_tasks.py b/enhydris/autoprocess/tests/test_tasks.py
new file mode 100644
index 00000000..dbe6611d
--- /dev/null
+++ b/enhydris/autoprocess/tests/test_tasks.py
@@ -0,0 +1,29 @@
+from io import StringIO
+from unittest import mock
+
+from django.test import TestCase
+
+from model_bakery import baker
+
+from enhydris.autoprocess.models import Checks
+from enhydris.autoprocess.tasks import execute_auto_process
+
+
+class ExecuteAutoProcessTaskTestCase(TestCase):
+    @mock.patch("enhydris.autoprocess.models.tasks.execute_auto_process")
+    def setUp(self, m):
+        self.auto_process = baker.make(Checks)
+        self.target_timeseries = self.auto_process.target_timeseries
+        self.target_timeseries.insert_or_append_data(
+            StringIO("2020-01-01 00:00,10,\n"), default_timezone="UTC"
+        )
+
+    @mock.patch("enhydris.autoprocess.models.Checks.execute")
+    def test_calls_execute_with_recalculate_true(self, m):
+        execute_auto_process(self.auto_process.id, has_non_append_modifications=True)
+        m.assert_called_once_with(recalculate=True)
+
+    @mock.patch("enhydris.autoprocess.models.Checks.execute")
+    def test_calls_execute_with_recalculate_false(self, m):
+        execute_auto_process(self.auto_process.id, has_non_append_modifications=False)
+        m.assert_called_once_with(recalculate=False)
diff --git a/enhydris/models/timeseries.py b/enhydris/models/timeseries.py
index 0e9a1f9d..65bf65ae 100644
--- a/enhydris/models/timeseries.py
+++ b/enhydris/models/timeseries.py
@@ -76,6 +76,15 @@ def get_default_publicly_available():
 class Timeseries(models.Model):
     timeseriesrecord_set: models.Manager["TimeseriesRecord"]
 
+    # When the calculation of derivative time series (e.g. checked, regularized,
+    # aggregated) is triggered, it is performed on the newer data only; the older data
+    # is left as is. This does not work if the modification of the source time series
+    # (i.e. this timeseries) is anything other than append (e.g. if data is inserted in
+    # the middle of the time series, or if some records are deleted). In this case, the
+    # derivative time series should be fully recalculated.  The
+    # has_non_append_modifications attribute is used to signal this case.
+    has_non_append_modifications: bool = False
+
     INITIAL = 100
     CHECKED = 200
     REGULARIZED = 300
@@ -290,7 +299,7 @@ def set_data(
         default_timezone: str | None = None,
     ):
         self.timeseriesrecord_set.all().delete()
-        return self.insert_or_append_data(data, default_timezone)
+        return self.insert_or_append_data(data, default_timezone, append_only=False)
 
     def insert_or_append_data(
         self,
@@ -299,6 +308,8 @@ def insert_or_append_data(
         append_only: bool = True,
     ):
         ahtimeseries = self._get_htimeseries_from_data(data, default_timezone)
+        if not append_only:
+            self.has_non_append_modifications = True
         if append_only:
             self._check_new_data_is_newer(ahtimeseries)
         result = TimeseriesRecord.bulk_insert(self, ahtimeseries)
diff --git a/enhydris/tests/test_models/test_timeseries.py b/enhydris/tests/test_models/test_timeseries.py
index e7afce4a..06b4d9f6 100644
--- a/enhydris/tests/test_models/test_timeseries.py
+++ b/enhydris/tests/test_models/test_timeseries.py
@@ -15,7 +15,7 @@
 from model_bakery import baker
 
 from enhydris import models
-from enhydris.tests import ClearCacheMixin, TestTimeseriesMixin
+from enhydris.tests import ClearCacheMixin, TestTimeseriesMixin, TimeseriesDataMixin
 
 
 def get_tzinfo(tzname: str):
@@ -714,6 +714,41 @@ def test_disallows_overwrite(self):
             )
 
 
+class TimeseriesHasNonAppendModificationsTestCase(TimeseriesDataMixin, TestCase):
+    def setUp(self):
+        self.create_timeseries()
+
+    def test_default_value_is_false(self):
+        timeseries = baker.make(models.Timeseries)
+        self.assertFalse(timeseries.has_non_append_modifications)
+
+    def test_append_keeps_value_false(self):
+        self.timeseries.has_non_append_modifications = False
+        self.timeseries.insert_or_append_data(
+            StringIO("2019-01-01 01:00,43,\n"),
+            default_timezone=self.timezone,
+            append_only=True,
+        )
+        self.assertFalse(self.timeseries.has_non_append_modifications)
+
+    def test_insert_sets_value_true(self):
+        self.timeseries.has_non_append_modifications = False
+        self.timeseries.insert_or_append_data(
+            StringIO("2019-01-01 01:00,43,\n"),
+            default_timezone=self.timezone,
+            append_only=False,
+        )
+        self.assertTrue(self.timeseries.has_non_append_modifications)
+
+    def test_set_data_sets_value_true(self):
+        self.timeseries.has_non_append_modifications = False
+        self.timeseries.set_data(
+            StringIO("2018-01-01 00:00,42,\n"),
+            default_timezone=self.timezone,
+        )
+        self.assertTrue(self.timeseries.has_non_append_modifications)
+
+
 class TimeseriesGetLastRecordAsStringTestCase(TestTimeseriesMixin, TestCase):
     def test_when_record_exists(self):
         self._create_test_timeseries("2017-11-23 17:23,1,\n2018-11-25 01:00,2,\n")