A CPM/PERT network consists of branches and nodes and depicts the precedence relationships between activities. The Gantt chart does not clearly show precedence relationships, which can be a disadvantage when using it for small projects. However, CPM/ PERT also has certain limitations. The project manager tends to rely so heavily on the project network that errors in the precedence relationship or missing activities can be overlooked; attention to critical path activities can become excessive to the extent that other project activities may be neglected or delayed.
Both CPM and PERT were derived from the Gantt chart and so were very similar. However, there were originally two primary differences between CPM and PERT. CPM used a single estimate for activity time that did not allow for any variation and treated activity times as if they were known for certain, or "deterministic." PERT used multiple time estimates for each activity that allowed for variation, and so they were treated as "probabilistic." The other difference was that they used different conventions for constructing a network. With CPM, the nodes (circles) represented the project activities. The arrows in between the nodes indicated the precedence relationships between activities. This approach to network construction was called activity-on-node (AON). With PERT, the opposite convention was taken. The branches represented the activities, and the nodes in between them reflected events or points in time such as the end of one activity and the beginning of another. This approach was referred to as activity-on-arrow (AOA).
Over time, however, CPM and PERT merged into a single technique now referred to as CPM/PERT.
Global projects involving companies and team members from different countries have grown as a result of increased information and communication technology. While a globally diverse project team can have advantages, issues can arise that affect project work and the success of the project. English is generally accepted and used globally to conduct business, so language will not necessarily be an issue. Instead, issues may arise from things such as differing attitudes toward work and vacation time, differing management styles, and differing ways of addressing problems. Or some people may simply have trouble working with others from different cultures. Whatever the issues, identifying and addressing these issues in a global project group is critical for project management and for achieving project success.