The above figure is an example of a network or arrow diagram used in developing an electronic component for a complex system. Each circle on the diagram represents the a task or well-defined activity that is part of the project. The number above each arrow represents the expected time required to complete the path from one task to another.

To go from Task A to Task B requires one week to complete and might, for example, represent the development of general specifications. Arrows indicate the precedence of relationships and depict which tasks must be completed before subsequent task can begin. In the example, tasks B, C, and D cannot be started until A has been completed.

Task H cannot be started until parts A, B, C, D, E, F and G are completed. This could be one of the final phases of the product such as testing. Without the previous steps, the project cannot be tested. The arrow diagram helps us determine how long a project will take to complete. Adding all of the task times together in the example indicates there are 33 weeks of work to be completed. However, several tasks can be done simultaneously. For example, once task A is finished, B, C, and D can be started and worked on at the same time. Thus, the earliest completion date can be determined by looking at all possible paths through the network and choosing the longest one, or the one with tasks requiring the most total time. In this example, the longest or critical path is A-C-F-H taking a total of 13 weeks to complete.

The arrow diagram also gives more information to the project planner. The earliest possible time that task H can be started is in 10 weeks after the start of the project (after tasks A, C, and F have been completed). When task A is completed, tasks B and E do not have to be started immediately in order to complete the project in the minimum possible time. Task B has four weeks of slack and E has one week of slack. The diagram shows that if activity B is started four weeks later than its earliest possible start time, then task E would then be started after Task B. This still allows H to be completed at its earliest time, after 10 weeks. Slack in a project network is a powerful concept that allows planners to schedule scarce resources efficently and manage people and equipment so that critical activities are kept on schedule and slack activites are delayed without placing the project in jeopardy. This simple example is based on CPM logic; it uses single-point task time estimates and assumes that the completion time for the project is the sum of the task times along the critical path.