According to the PMBOK® Guide, specifically within the Monitor and Control Project Work and Earned Value Management (EVM) sections, the Performance Measurement Baseline (PMB) is the primary tool used to measure project success.

Integration of Triple Constraints: The PMB is an approved, integrated plan for the project work against which project execution is compared, and deviations are measured for management control. It specifically integrates three key baselines:

Scope Baseline: The approved version of the scope statement, WBS, and WBS dictionary.

Schedule Baseline: The approved version of the schedule model.

Cost Baseline: The approved version of the time-phased project budget.

Earned Value Management (EVM): In EVM, the PMB is used as the " Planned Value " (PV) to compare against " Actual Cost " (AC) and " Earned Value " (EV). By integrating these three parameters into one baseline, the project manager can see if the project is ahead/behind schedule relative to the budget spent and scope completed.

Approval: The PMB is typically established during the Planning phase and can only be changed through formal change control procedures.

Why the other options are incorrect:

B. Analysis of project forecasts: Forecasting (such as EAC or ETC) is a process or output of performance measurement, not the place where the original parameters are integrated into a baseline.

C. Summary of changes approved in a period: This is a report or log (Change Log) used to track modifications. While these changes might update the baseline, the summary itself is not the integrated baseline.

D. Analysis of past performance: This is a retrospective activity (like Trend Analysis) used to see how the project has performed so far. It uses the Performance Measurement Baseline as a reference point but is not the baseline itself.