I HAVE A LOGBOOK WHICH KEEPS THE RECORD OF ALL FAULT BOOKED BY DIFFERENT SUBSCRIBER.THIS LOGBOOK HAS THREE ATTRIBUTE DOWNTIME,UPTIME & TOTAL DURATION (DATE &TIME FORMAT) . I WANT TO CALCULATE THE TOTAL DURATION AUTOMATICALLY WHENEVR UPTIME VALUE IS GIVEN AND IF THE UPTIME IS NOT GIVEN IT SHOULD CALCULATE DEPENDING UPON THE SYSTEM PRESENT TIME.PLEAS EXPLAIN IT WITH EXAMPLE.