The EPC Level 1 schedule summarizes the overall project for client and management. EPC Level 1 schedules show start and finish dates for the major project phases and key milestones (such as design, procurement, construction, and commissioning and start-up). Significant contract milestones and project-specific milestones or activities are included in EPC Level 1 schedules as required by the project execution plan. EPC Level 2 schedules contain more detailed activities for each of the summary phases previously identified in the Level 1 schedule. This often includes a breakout of the various trades or disciplines responsible for the activities in each phase, the critical procurement activities, the major elements of construction, and general commissioning and start-up requirements. Generally in the EPC Level 2, this is the first level of scheduled detail where logical links or task relationships may be shown.EPC Level 3 is the first level where the full use of critical path method (CPM) techniques could be shown effectively. In addition to start and finish dates for each grouping of deliverables or activities within each phase of the project, EPC Level 3 schedules include major review and approval dates as well. Most EPC schedule models are not developed below Level 3 in terms of CPM activity detail, with the intent to keep the schedule broad enough to be described for any specific project. Since EPC schedule levels are normally limited to Levels 1 through 3, sometimes an ‘external’ schedule or set of schedules would be included for a project. These external schedules are called “Level 4.” EPC Level 4 are detailed work schedules and generally would be prepared outside of the CPM software, with careful correlation to the CPM schedule activities and scope of work. The theory is, that if there is too much detail within the CPM network, the schedule would not only lose its flexibility as a value-added tool to manage the job, but schedule maintenance would become difficult, due to the greater effort needed to maintain the CPM logic after each progress update. A variety of software tools can be employed to develop work schedules at Level 4 and below: spreadsheets, databases, and word processing are all utilized.