What is differences between L3 and L4 project schedue, and which level do you use to create a 1 month look ahead program?

Level3 Schedule:

Project Coordination Schedule (PCS) also called a Publication Schedule. Initially developed as an integrated CPM overview of the project, the Level3 schedule is then maintained as an integrated rollup or summary of the Level4 schedule activities for reporting status to senior management and to report monthly status to major clients, etc.

Level4 Schedule:

Execution Schedule, also called a Project Working Level Schedule. Level4 is the detailed working level schedule, where each schedule is an expansion of part of a Level3 schedule, and is established within the integrated project schedule.

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