diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/activities/charts/AbstractChartFragment.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/activities/charts/AbstractChartFragment.java
index 5a3c8851..24519224 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/activities/charts/AbstractChartFragment.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/activities/charts/AbstractChartFragment.java
@@ -40,10 +40,28 @@ import nodomain.freeyourgadget.gadgetbridge.model.ActivitySample;
 import nodomain.freeyourgadget.gadgetbridge.util.DateTimeUtils;
 import nodomain.freeyourgadget.gadgetbridge.util.DeviceHelper;
 
+/**
+ * A base class fragment to be used with ChartsActivity. The fragment can supply
+ * a title to be displayed in the activity by returning non-null in #getTitle()
+ * Broadcast events can be received by overriding #onReceive(Context,Intent).
+ * The chart can be refreshed by calling #refresh()
+ * Implement refreshInBackground(DBHandler, GBDevice) to fetch the samples from the DB,
+ * and add the samples to the chart. The actual rendering, which must be performed in the UI
+ * thread, must be done in #renderCharts().
+ * Access functionality of the hosting activity with #getHost()
+ *
+ * The hosting ChartsHost activity provides a section for displaying a date or date range
+ * being the basis for the chart, as well as two buttons for moving backwards and forward
+ * in time. The date is held by the activity, so that it can be shared by multiple chart
+ * fragments. It is still the responsibility of the (currently visible) chart fragment
+ * to set the desired date in the ChartsActivity via #setDateRange(Date,Date).
+ * The default implementations #handleDatePrev(Date,Date) and #handleDateNext(Date,Date)
+ * shift the date by one day.
+ */
 public abstract class AbstractChartFragment extends AbstractGBFragment {
     protected int ANIM_TIME = 350;
 
-    private static final Logger LOG = LoggerFactory.getLogger(ActivitySleepChartFragment.class);
+    private static final Logger LOG = LoggerFactory.getLogger(AbstractChartFragment.class);
 
     private final Set<String> mIntentFilterActions;
     private BroadcastReceiver mReceiver = new BroadcastReceiver() {
@@ -102,43 +120,6 @@ public abstract class AbstractChartFragment extends AbstractGBFragment {
         LocalBroadcastManager.getInstance(getActivity()).registerReceiver(mReceiver, filter);
     }
 
-    @Override
-    public void onHiddenChanged(boolean hidden) {
-        super.onHiddenChanged(hidden);
-    }
-
-    @Override
-    public void onPause() {
-        super.onPause();
-    }
-
-    @Override
-    public void onResume() {
-        super.onResume();
-    }
-
-    @Override
-    public void onStart() {
-        super.onStart();
-    }
-
-    @Override
-    public void onStop() {
-        super.onStop();
-    }
-
-    @Override
-    public void setUserVisibleHint(boolean isVisibleToUser) {
-        super.setUserVisibleHint(isVisibleToUser);
-    }
-
-//    @Override
-//    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
-//        View view = super.onCreateView(inflater, container, savedInstanceState);
-//        updateDateInfo(mStartDate, mEndDate);
-//        return view;
-//    }
-
     private void setStartDate(Date date) {
         getHost().setStartDate(date);
     }
@@ -186,16 +167,32 @@ public abstract class AbstractChartFragment extends AbstractGBFragment {
         }
     }
 
+    /**
+     * Default implementation shifts the dates by one day, if visible
+     * and calls #refreshIfVisible().
+     * @param startDate
+     * @param endDate
+     */
     protected void handleDatePrev(Date startDate, Date endDate) {
         if (isVisibleInActivity()) {
-            shiftDates(startDate, endDate, -1);
+            if (!shiftDates(startDate, endDate, -1)) {
+                return;
+            }
         }
         refreshIfVisible();
     }
 
+    /**
+     * Default implementation shifts the dates by one day, if visible
+     * and calls #refreshIfVisible().
+     * @param startDate
+     * @param endDate
+     */
     protected void handleDateNext(Date startDate, Date endDate) {
         if (isVisibleInActivity()) {
-            shiftDates(startDate, endDate, +1);
+            if (!shiftDates(startDate, endDate, +1)) {
+                return;
+            }
         }
         refreshIfVisible();
     }
@@ -208,11 +205,18 @@ public abstract class AbstractChartFragment extends AbstractGBFragment {
         }
     }
 
-    protected void shiftDates(Date startDate, Date endDate, int offset) {
+    /**
+     * Shifts the given dates by offset days. offset may be positive or negative.
+     * @param startDate
+     * @param endDate
+     * @param offset a positive or negative number of days to shift the dates
+     * @return true if the shift was successful and false otherwise
+     */
+    protected boolean shiftDates(Date startDate, Date endDate, int offset) {
         Date newStart = DateTimeUtils.shiftByDays(startDate, offset);
         Date newEnd = DateTimeUtils.shiftByDays(endDate, offset);
 
-        setDateRange(newStart, newEnd);
+        return setDateRange(newStart, newEnd);
     }
 
     protected Integer getColorFor(int activityKind) {
@@ -326,7 +330,7 @@ public abstract class AbstractChartFragment extends AbstractGBFragment {
     protected abstract void refreshInBackground(DBHandler db, GBDevice device);
 
     /**
-     * Performs a re-rendering of the chart.
+     * Triggers the actual (re-) rendering of the chart.
      * Always called from the UI thread.
      */
     protected abstract void renderCharts();
@@ -441,6 +445,14 @@ public abstract class AbstractChartFragment extends AbstractGBFragment {
         }
     }
 
+    /**
+     * Implement this to supply the samples to be displayed.
+     * @param db
+     * @param device
+     * @param tsFrom
+     * @param tsTo
+     * @return
+     */
     protected abstract List<ActivitySample> getSamples(DBHandler db, GBDevice device, int tsFrom, int tsTo);
 
     protected abstract void setupLegend(Chart chart);
@@ -526,12 +538,23 @@ public abstract class AbstractChartFragment extends AbstractGBFragment {
         }
     }
 
-    public void setDateRange(Date from, Date to) {
+    /**
+     * Returns true if the date was successfully shifted, and false if the shift
+     * was ignored, e.g. when the to-value is in the future.
+     * @param from
+     * @param to
+     */
+    public boolean setDateRange(Date from, Date to) {
         if (from.compareTo(to) > 0) {
             throw new IllegalArgumentException("Bad date range: " +from + ".." + to);
         }
+        Date now = new Date();
+        if (to.after(now)) {
+            return false;
+        }
         setStartDate(from);
         setEndDate(to);
+        return true;
     }
 
     protected void updateDateInfo(Date from, Date to) {