Critical Path Analysis

• The critical path identifies the sequence of tasks that will take the longest amount of time to complete, and any delay or disruption along this path can cause delays in completing the entire project.
• A critical activity cannot start until all its predecessor activities are completed.
• Critical path analysis is used to identify the critical activities that must be completed on time to ensure project success.
• Critical activities have zero slack (float) because they must be performed on schedule to ensure timely completion of the project.
• Non-critical activities have positive float/slack, meaning there is some flexibility in their scheduling without affecting the overall project duration.
• Non-critical activities have some flexibility in terms of timing without affecting the overall completion date of the project.
• Total slack (TS) is calculated by subtracting the early finish time from the late finish time.
• Slack refers to the amount of time an activity can be delayed without causing a delay in the project's completion date.
• Total Float is the maximum allowable delay in starting an activity without impacting the project end date.
• Free Float is the amount of time an activity can be delayed beyond its early start time without delaying the early start times of other downstream activities.
• Arcs represent the activities
• Arc weights show the duration of the activities
• Nodes are used to indicate the beginning or ending point of an arc, as well as intermediate points along the path
• Critical path analysis involves identifying the longest sequence of interdependent tasks that must be completed sequentially within a given period of time
• The network must have a single start and a single finish event
• The network must be simple
• There is no cycle in the network
• Each activity has only one predecessor and successor
• Forward passes uses the largest possible number on the way forward
• Backward pass uses the smallest possible number on the way back
• Dummy activities may be needed to form a simple digraph either to ensure all dependent activities are completed prior to starting the next activity or to ensure a unique numbering for activities
• Critical path analysis can be used to determine the critical path, which is the longest path through the project.
• A dummy activity is an activity that has 0 duration
• Dummy activities are shown as a dashed line
• The least possible number of dummies must be used
• The float of an activity is the amount of time that its start may be delayed without affecting the duration of the project
• Total float = latest finish - earliest start - duration
• The total float of any critical activity is 0
• Total float = independent float + interfering float
• Independent floats have no knock on effect on other floats
• Interfering floats have a knock on effect on other floats
• Independent float is maximum amount of time an activity can be delayed without affecting the early start of the next activities, and without being affected by the allowable delay of any previous activities
• Interfering float is the amount of time an activity can be delayed from its earliest start time without delaying the duration of the project
• Using up interfering floats EATS INTO the float of the following activities
• A Cascade Diagram/Gantt Chart provides a graphical way to represent the range of possible start and finish times for all activities on a single diagram
• The number scale of a Gantt Chart shows elapsed time
• Critical activities on a Gantt Chart are shown as rectangles lined up together in a line
• Non-critical activities on a Gantt chart have some slack or float between them
• Slack (float) is measured along the horizontal axis of a Gantt chart
• The total float of each activity is represented by the range of movement of its rectangle on the chart shown as a dotted box