diff --git a/modules/time-calc-app/src/main/java/org/nanoboot/utils/timecalc/swing/common/MainWindow.java b/modules/time-calc-app/src/main/java/org/nanoboot/utils/timecalc/swing/common/MainWindow.java
index 5e2c33f..182e3a7 100644
--- a/modules/time-calc-app/src/main/java/org/nanoboot/utils/timecalc/swing/common/MainWindow.java
+++ b/modules/time-calc-app/src/main/java/org/nanoboot/utils/timecalc/swing/common/MainWindow.java
@@ -529,13 +529,18 @@ public class MainWindow extends TWindow {
             //System.out.println("timeCalcConfiguration.handsLongProperty=" + timeCalcConfiguration.clockHandLongProperty.isEnabled());
 
             {
+
                 TTime startTime = arrivalTextField.asTimeHM();
                 TTime overtime = overtimeTextField.asTimeHM();
-                departureTextField.valueProperty.setValue(new TTime(
-                        startTime.getHour() + Constants.WORKING_HOURS_LENGTH + overtime
-                                .getHour(),
-                        startTime.getMinute() + Constants.WORKING_MINUTES_LENGTH
-                        + overtime.getMinute()).toString().substring(0, 5));
+                TTime newDeparture = startTime.add(new TTime(8,30));
+                if(overtime.isNegative()) {
+                    TTime tmpTTime = overtime.cloneInstance();
+                    tmpTTime.setNegative(false);
+                    newDeparture = newDeparture.remove(tmpTTime);
+                } else {
+                    newDeparture = newDeparture.add(overtime);
+                }
+                departureTextField.valueProperty.setValue(newDeparture.toString().substring(0, 5));
             }
             Visibility currentVisibility = Visibility
                     .valueOf(timeCalcApp.visibilityProperty.getValue());
diff --git a/modules/time-calc-app/src/main/java/org/nanoboot/utils/timecalc/utils/common/TTime.java b/modules/time-calc-app/src/main/java/org/nanoboot/utils/timecalc/utils/common/TTime.java
index 909a8ba..5c2d918 100644
--- a/modules/time-calc-app/src/main/java/org/nanoboot/utils/timecalc/utils/common/TTime.java
+++ b/modules/time-calc-app/src/main/java/org/nanoboot/utils/timecalc/utils/common/TTime.java
@@ -103,10 +103,10 @@ public class TTime implements Comparable<TTime> {
         this(false, hourIn, minuteIn, secondIn, millisecondIn);
     }
     public TTime(boolean negative, int hourIn, int minuteIn, int secondIn, int millisecondIn) {
-        this.hour = hourIn;
-        this.minute = minuteIn;
-        this.second = secondIn;
-        this.millisecond = millisecondIn;
+        this.hour = Math.abs(hourIn);
+        this.minute = Math.abs(minuteIn);
+        this.second = Math.abs(secondIn);
+        this.millisecond = Math.abs(millisecondIn);
         this.negative = negative;
         while (minute >= MINUTES_PER_HOUR) {
             minute = minute - MINUTES_PER_HOUR;
@@ -125,7 +125,7 @@ public class TTime implements Comparable<TTime> {
         return result;
     }
 
-    private static TTime ofMilliseconds(int s) {
+    public static TTime ofMilliseconds(int s) {
         int hours = s / 60 / 60 / 1000;
         int milliseconds = s - hours * 60 * 60 * 1000;
         int minutes = milliseconds / 60 / 1000;
@@ -138,12 +138,12 @@ public class TTime implements Comparable<TTime> {
 
     public TTime add(TTime tTimeToBeAdded) {
         TTime result = this.cloneInstance();
-//        if(result.isNegative()) {
-//            result.setNegative(false);
-//            result.remove(tTimeToBeAdded);
-//            result.setNegative(true);
-//            return result;
-//        }
+        if(result.isNegative()) {
+            result.setNegative(false);
+            result = result.remove(tTimeToBeAdded);
+            result.setNegative(result.toTotalMilliseconds() != 0);
+            return result;
+        }
         Calendar cal = asCalendar();
         cal.add(Calendar.HOUR_OF_DAY, tTimeToBeAdded.hour);
         cal.add(Calendar.MINUTE, tTimeToBeAdded.minute);