S-Curve
An S-curve is a graphical display of cumulative costs, labor hours, or other quantities plotted against time, forming a characteristic S-shape.
Explanation
The S-curve gets its name from the typical shape of cumulative project spending over time. Spending starts slowly during project initiation and planning, accelerates during execution as the majority of work is performed, and then tapers off during closing as the project winds down.
In earned value management, the S-curve is used to display the cost baseline (PV plotted over time), earned value (EV plotted over time), and actual cost (AC plotted over time) on the same graph. This visual representation makes it easy to identify schedule and cost variances at any point. The gap between the PV and EV curves shows schedule variance, while the gap between the EV and AC curves shows cost variance.
S-curves are also used for funding limit reconciliation, where the cumulative cost baseline is compared with funding step functions to ensure adequate funding is available at each stage of the project.
Key Points
- •Shows cumulative costs or progress plotted against time
- •Named for its characteristic S-shaped curve
- •Used in EVM to display PV, EV, and AC simultaneously
- •Visual gaps between curves reveal schedule and cost variances
Exam Tip
On an S-curve, the vertical gap between PV and EV at any point is SV, and the vertical gap between EV and AC is CV. Be able to read variances from an S-curve diagram.
Frequently Asked Questions
Related Topics
Cost Baseline
The cost baseline is the approved version of the time-phased project budget, excluding management reserves, used as a reference for measuring and monitoring cost performance.
Earned Value Management (EVM)
Earned Value Management (EVM) is a methodology that integrates scope, schedule, and cost data to assess project performance and progress objectively.
Funding Requirements
Funding requirements define the total and periodic funding needs derived from the cost baseline, including projected expenditures plus anticipated liabilities.
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