Scheduling and Cost Control
Scheduling Fundamentals
The critical path method (CPM) identifies the longest sequence of dependent activities; that path determines project duration. Float (slack) is the amount of time an activity can slip without delaying the project. Critical activities have zero float. Understand dependencies (finish-to-start and variants), lag, and lead. Gantt charts visualize; network diagrams reveal logic and float.
Cost Control
Budgets are baselines. Track committed, actual, and forecast costs. Earned value management (EVM) gives early warning: cost variance (CV = EV − AC) and schedule variance (SV = EV − PV); cost performance index (CPI = EV/AC) and schedule performance index (SPI = EV/PV). A CPI below 1 means spending more than earned; an SPI below 1 means behind schedule. Forecast at completion using EVM ratios.
Productivity and Contingency
Track labour productivity against estimates; use contingency for known risks and management reserve for unknown ones. Distinguish direct costs, indirect costs, and overhead.
Traps
Questions confuse float with total duration, or assume the longest-duration activity is always critical-only the longest path is. Another trap: treating SV as a cost measure; it is schedule variance expressed in money. Beware interpreting a positive CV as "ahead of schedule"-that is SV.
Rule of Thumb
Critical path = zero float; CPI and SPI tell you which problem you have. Worked example: EV = 400, AC = 450, PV = 500. CV = −50 (over budget), SV = −100 (behind schedule), CPI = 0.89, SPI = 0.80. The project is both over budget and behind; investigate cost drivers and schedule slippage separately.