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The following priority sequencing rules are generally followed in reduction/service system:

  1. 1.   First Come First Served (FCFS). As explained earlier, it is followed to avoid any heart bums at avoidable controversies.
  2. 2.   Earliest Due Date (EDD). In this rule; top priority is allotted to the waiting job which has the earliest due/delivery date. In this case the order of arrival of the job and processing time it takes is ignored.
  3. 3.   Least Slack Rule (LS). It gives top priority to the waiting job whose slack time is the least. Slack time is the difference between the length of time remaining until the job is due and the length of it operation time.
  4. 4.   Average Number of Jobs in the System. It is defined as the average number of jobs remaining in the system (waiting or being processed) from the beginning of sequence through the time when the last job is finished.
  5. 5.   Average Job Lateness. Jobs lateness is defined as the difference between the actual completion time of the job and its due date. Average job lateness is sum of lateness of all jobs divided by the number of jobs in the system. This is also called Average Job Tardiness.
  6. 6.   Average Earliness of Jobs. If a job is completed before its due date, the lateness value is negative and the magnitude is referred as earliness of job. Mean earliness of the job is the sum of earliness of all jobs divided by the number of jobs in the system.
  7. 7.   Number of Tardy Jobs. It is the number of jobs which are completed after the due date.