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usage of Gantt chart is that it can provide an overview of the project activities and their inner relationships and then to make a plan. Furthermore, using Gantt chart can also make analysis about the whole schedule plan, such as critical path calculation and total duration evaluation. In project operation stage, Gantt chart is also a useful tool in order to draw a clear conclusion about the deviation between the planned schedule and the recent one. To identify this kind of deviation is the foundation of adjustment, so as to keep the project run to the right way.

Compared with other schedule plan techniques such as PERT, there are several benefits when using Gantt chart. First of all, when dealing with small and medium sized projects, it can provide an excellent graphic image which is much easier to understand. Second, Gantt chart can be supported by some special project management software to realize complex calculations and complex dependencies and conduct “what-if” analysis (Harvey, 2011).

However, as a kind of primary project management tool which is developed for such a long time, Gantt chart has some limitations when dealing with complex problems. Especially for this modern society, more and more complex projects appeared. They are often considerably more complex than can be communicated effectively by a Gantt chart. Moreover, Gantt chart only represents few parts of project management field. It mainly focuses on schedule management but according to PMBOK, project management is composed by nine parts. And there are some researchers argued that Gantt chart do not represent the size of the project or the relative size of work elements, therefore the magnitude of a behind-schedule condition can be easily misunderstood (Stephen, 2011).

3.3 Program Evaluation and Review Technique (PERT)
Program Evaluation and Review Technique (PERT) is a kind of useful technology which is used in schedule planning and optimizing. It is developed in the late 1950’s for the US Navy’s Polaris project which had thousands of contractors. Based on the duration and the precedence relationship of those tasks, it can optimize the total duration and make a proper arrangement about each task’s position in the whole schedule plan.

PERT is focus on the mile stone task (or time point) and the critical path which is consisted of a series of tasks that direct related to the total duration. The mile stone event represents some key points in schedule management that in these key points, to compare with the planed performance and the real one will let the project manager know exactly the project’s progress and potential risks. Those tasks in critical path should not be changed easily because a slight change will cause the whole schedule plan facing readjust risk. Of course on the other hand, to short the duration of tasks in critical path is the only way to short the whole duration of project. In addition, it should be stated that not like the Gantt Chart, those task durations in PERT are all expected value but not a precise pre-evaluation. So, the real value of duration is uncertain which means in the project management practice (Maria etc., 2011), readjustment should be considered first in the schedule planning.

PERT consists of several steps to complete a project plan. First of all, and also the fundamental of PERT process is to identify specific activities, the