Activities & Critical Path Method (CPM)

Now that your project structure is ready, it's time to breathe life into it. We'll add activities, assign durations, and — most importantly — connect them with logical relationships so P6 can calculate the schedule automatically.

1. The 6 Activity Types

Type	How P6 Calculates Duration	Construction Usage
Task Dependent	Fixed duration — uses project calendar	99% of activities: excavation, pouring, installation
Resource Dependent	Driven by resource calendar	Rare: exclusive tower crane
Level of Effort (LOE)	Elastic — never critical	Overhead: security, supervision, management
Start Milestone	Zero duration — marks a beginning	Notice to Proceed (NTP)
Finish Milestone	Zero duration — marks an end	Provisional Handover
WBS Summary	Auto-summary of a WBS package	Not recommended

2. Logical Relationships

Type	Meaning	Example
FS (Finish-to-Start)	Successor starts after predecessor finishes (most common)	Pour concrete → Strip formwork
SS (Start-to-Start)	Both start in parallel	Dig trench ← backfill behind
FF (Finish-to-Finish)	Both finish together	Install cables ← test cables
SF (Start-to-Finish)	Very rare	—

Lag (+): Waiting period (e.g., curing). Lead (-): Overlap (most clients prohibit it).

3. Constraints

• Start On or After: For the first activity (Data Date).
• Finish On or Before: For final milestones (contractual deadline).
• As Late As Possible: For procurement activities.

4. CPM Calculation

Press F9 to schedule. P6 calculates:

Total Float = 0 or negative → This is the Critical Path (shown in red on Gantt). As a planner, this red line is your #1 priority day and night.