Planners must estimate the tolerance time of each process and what process is the bottleneck of the work without affecting the final project duration, and arrange the scheme of each process and the effective utilization of manpower and resources in the plan accordingly. PERT includes three steps in the "management cycle": planning, implementation and control.
2. Gantt chart, also known as bar chart. It was developed by henry gantt in 19 17. Its internal thinking is very simple, basically a line chart. The horizontal axis represents time, the vertical axis represents activities (projects), and the lines represent the planned and actual completion of activities during the whole period. It intuitively shows when the task plan will be executed and the comparison between the actual progress and the planned requirements.
Managers can easily find out what work remains to be done in a task (project), and can evaluate whether the work is ahead of schedule or behind schedule, or whether it is going on normally. It is an ideal control tool.
The meaning of Gantt Chart
Gantt chart contains the following three meanings:
1. Display activities in the form of graphs or tables;
2. Now this is a general method to show the progress;
3. The actual calendar day and duration should be included in the construction, and weekends and holidays should not be included in the schedule.
Gantt chart is simple, eye-catching and easy to compile, and is widely used in enterprise management. Gantt chart can be divided into five forms according to different contents: plan chart, load chart, machine idle chart, personnel idle chart and schedule plan.
It first appeared in 1950s. It is a kind of network analysis, which predicts the project duration by analyzing which activity sequence has the smallest total time difference in the project process. Its usual practice is:
1) treats all activities in the project as nodes with time attributes, and arranges them from the start point to the end point of the project; 2) Labeling the relationship between the immediately preceding activity and the immediately following activity of each node with directed line segments to make it a directed network graph; 3) Calculate the earliest start time, the latest start time, the earliest finish time and the latest finish time of each activity through forward deduction and reverse deduction, and calculate the time difference of each activity; 4) Find out the route composed of all activities with zero time difference, that is, the critical path; 5) Determine the quasi-critical path to provide constraints for network optimization;
Features:
The duration of activities on the critical path determines the duration of the project, and the total duration of all activities on the critical path is the duration of the project.
Any activity on the critical path is a critical activity, and the delay of any activity will lead to the delay of the completion time of the whole project.
The time spent on the critical path is the shortest time that can be completed. If the total time spent on the critical path is shortened, the duration of the project will also be shortened. Otherwise, the total duration of the whole project will be extended. However, if the time required for various activities on the non-critical path is shortened, the completion time of the project will not be affected.
The activity on the critical path is the activity with the smallest total time difference, and the time-consuming to change one of the activities may change the critical path. There can be multiple critical paths, and their total time must be equal, that is, the total duration of completion.
The critical path is relative or variable. After taking certain technical organization measures, the critical path may become a non-critical path, and the non-critical path may also become a critical path.