diff --git a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/zoom/DetailThreeTimeTrackerState.java b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/zoom/DetailThreeTimeTrackerState.java
index 6df6454c6..19e9cdccd 100644
--- a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/zoom/DetailThreeTimeTrackerState.java
+++ b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/zoom/DetailThreeTimeTrackerState.java
@@ -1,87 +1,49 @@
 package org.zkoss.ganttz.util.zoom;
 
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Date;
-import java.util.List;
-
 import org.joda.time.DateTime;
 import org.joda.time.LocalDate;
 import org.joda.time.Months;
 import org.joda.time.ReadablePeriod;
-import org.zkoss.ganttz.util.Interval;
 import org.zkoss.util.Locales;
 
 /**
  * Zoom level with semesters in the first level and months in the second level
  * @author Óscar González Fernández <ogonzalez@igalia.com>
  */
-public class DetailThreeTimeTrackerState extends TimeTrackerState {
+public class DetailThreeTimeTrackerState extends TimeTrackerStateUsingJodaTime {
 
     public static final DetailThreeTimeTrackerState INSTANCE = new DetailThreeTimeTrackerState();
 
     private static final int FIRST_LEVEL_SIZE = 300;
     protected static final int SECOND_LEVEL_SIZE = 50;
 
-    private static LocalDate asLocalDate(Date date) {
-        return new LocalDate(date);
-    }
-
-    public interface IDetailItemCreator {
-        DetailItem create(DateTime dateTime);
-    }
-
-    public static Collection<DetailItem> createDetails(Interval interval,
-            ReadablePeriod period, IDetailItemCreator detailItemCreator) {
-        DateTime current = asLocalDate(interval.getStart())
-                .toDateTimeAtStartOfDay();
-        DateTime end = asLocalDate(interval.getFinish())
-                .toDateTimeAtStartOfDay();
-        List<DetailItem> result = new ArrayList<DetailItem>();
-        while (current.isBefore(end)) {
-            result.add(detailItemCreator.create(current));
-            current = current.plus(period);
-        }
-        return result;
-    }
-
     private DetailThreeTimeTrackerState() {
     }
 
     @Override
-    protected Collection<DetailItem> createDetailsForFirstLevel(
-            Interval interval) {
-        return createDetails(getRealIntervalFor(interval), Months.months(6),
-                new IDetailItemCreator() {
-
-                    @Override
-                    public DetailItem create(DateTime dateTime) {
-                        return new DetailItem(FIRST_LEVEL_SIZE,
-                                getYearWithSemesterString(dateTime));
-                    }
-                });
-    }
-
-    private String getYearWithSemesterString(DateTime dateTime) {
-        return dateTime.getYear() + ","
-                + (dateTime.getMonthOfYear() < 6 ? "H1" : "H2");
+    protected ReadablePeriod getPeriodFirstLevel() {
+        return Months.months(6);
     }
 
     @Override
-    protected Collection<DetailItem> createDetailsForSecondLevel(
-            Interval interval) {
-        return createDetails(getRealIntervalFor(interval), Months.months(1),
-                new IDetailItemCreator() {
-
-                    @Override
-                    public DetailItem create(DateTime dateTime) {
-                        return new DetailItem(SECOND_LEVEL_SIZE,
-                                getMonthString(dateTime));
-                    }
-                });
+    protected ReadablePeriod getPeriodSecondLevel() {
+        return Months.months(1);
     }
 
-    public LocalDate round(LocalDate date, boolean down) {
+    @Override
+    protected IDetailItemCreator getDetailItemCreatorSecondLevel() {
+        return new IDetailItemCreator() {
+
+            @Override
+            public DetailItem create(DateTime dateTime) {
+                return new DetailItem(SECOND_LEVEL_SIZE,
+                        getMonthString(dateTime));
+            }
+        };
+    }
+
+    @Override
+    protected LocalDate round(LocalDate date, boolean down) {
         if (date.getMonthOfYear() == 1 && date.getDayOfMonth() == 1)
             return date;
         if (date.getMonthOfYear() == 7 && date.getDayOfMonth() == 1)
@@ -95,15 +57,23 @@ public class DetailThreeTimeTrackerState extends TimeTrackerState {
         }
     }
 
-    @Override
-    public Interval getRealIntervalFor(Interval testInterval) {
-        LocalDate start = round(asLocalDate(testInterval.getStart()), true);
-        LocalDate finish = round(asLocalDate(testInterval.getFinish()), false);
-        return new Interval(start.toDateTimeAtStartOfDay().toDate(), finish
-                .toDateTimeAtStartOfDay().toDate());
-    }
-
     private String getMonthString(DateTime dateTime) {
         return dateTime.toString("MMM", Locales.getCurrent());
     }
-}
+
+    private String getYearWithSemesterString(DateTime dateTime) {
+        return dateTime.getYear() + ","
+                + (dateTime.getMonthOfYear() < 6 ? "H1" : "H2");
+    }
+
+    @Override
+    protected IDetailItemCreator getDetailItemCreatorFirstLevel() {
+        return new IDetailItemCreator() {
+            @Override
+            public DetailItem create(DateTime dateTime) {
+                return new DetailItem(FIRST_LEVEL_SIZE,
+                        getYearWithSemesterString(dateTime));
+            }
+        };
+    }
+}
\ No newline at end of file
diff --git a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/zoom/TimeTrackerStateUsingJodaTime.java b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/zoom/TimeTrackerStateUsingJodaTime.java
new file mode 100644
index 000000000..8aa123bba
--- /dev/null
+++ b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/zoom/TimeTrackerStateUsingJodaTime.java
@@ -0,0 +1,71 @@
+package org.zkoss.ganttz.util.zoom;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Date;
+import java.util.List;
+
+import org.joda.time.DateTime;
+import org.joda.time.LocalDate;
+import org.joda.time.ReadablePeriod;
+import org.zkoss.ganttz.util.Interval;
+
+/**
+ * @author Óscar González Fernández <ogonzalez@igalia.com>
+ */
+public abstract class TimeTrackerStateUsingJodaTime extends TimeTrackerState {
+
+    protected static LocalDate asLocalDate(Date date) {
+        return new LocalDate(date);
+    }
+
+    public interface IDetailItemCreator {
+        DetailItem create(DateTime dateTime);
+    }
+
+    public static Collection<DetailItem> createDetails(Interval interval,
+            ReadablePeriod period, IDetailItemCreator detailItemCreator) {
+        DateTime current = asLocalDate(interval.getStart())
+                .toDateTimeAtStartOfDay();
+        DateTime end = asLocalDate(interval.getFinish())
+                .toDateTimeAtStartOfDay();
+        List<DetailItem> result = new ArrayList<DetailItem>();
+        while (current.isBefore(end)) {
+            result.add(detailItemCreator.create(current));
+            current = current.plus(period);
+        }
+        return result;
+    }
+
+    @Override
+    protected Collection<DetailItem> createDetailsForFirstLevel(
+            Interval interval) {
+        return createDetails(getRealIntervalFor(interval),
+                getPeriodFirstLevel(), getDetailItemCreatorFirstLevel());
+    }
+
+    @Override
+    protected Collection<DetailItem> createDetailsForSecondLevel(
+            Interval interval) {
+        return createDetails(getRealIntervalFor(interval),
+                getPeriodSecondLevel(), getDetailItemCreatorSecondLevel());
+    }
+
+    protected abstract IDetailItemCreator getDetailItemCreatorFirstLevel();
+
+    protected abstract ReadablePeriod getPeriodFirstLevel();
+
+    protected abstract IDetailItemCreator getDetailItemCreatorSecondLevel();
+
+    protected abstract ReadablePeriod getPeriodSecondLevel();
+
+    protected abstract LocalDate round(LocalDate date, boolean down);
+
+    @Override
+    public Interval getRealIntervalFor(Interval testInterval) {
+        LocalDate start = round(asLocalDate(testInterval.getStart()), true);
+        LocalDate finish = round(asLocalDate(testInterval.getFinish()), false);
+        return new Interval(start.toDateTimeAtStartOfDay().toDate(), finish
+                .toDateTimeAtStartOfDay().toDate());
+    }
+}