The main weakness of Gantt chart is that it does not contain any information about the interrelationship of tasks to be performed. Although all tasks to be performed are listed on the chart, there is no way of telling if one task must be performed before another can be started. The program evaluation and review technique (PERT), a technique that evolved partly from the Gantt chart, is a scheduling tool that does emphasize the interrelationship of tasks.
But, what do we mean by PERT?
PERT is a network of project activities showing both the estimates of time necessary to complete each activity and the sequence of activities that must be followed to complete the project.