PSP — AACE Planning & Scheduling Professional Cheat Sheet

• CPM network calculation steps
• Float, logic, constraint, and calendar distinctions
• Schedule development and update workflow
• Baseline, progress, and forecast terminology
• Earned value and schedule-control formulas
• Resource, risk, and delay-analysis decision points

If the question gives activities starting at day 0, use elapsed-time math. If it gives work starting on day 1 and counts both first and last day, use inclusive math.

Core CPM Terms

CPM Fundamentals

Critical Path Method scheduling calculates early and late dates based on activity durations, logic, calendars, and constraints. The critical path is the longest path through the network to the project completion point, considering the schedule model rules.

Key CPM Terms

CPM Calculation Logic

For a simple finish-to-start network using the same calendar:

In real schedule software, calendars, relationship types, lag, constraints, and data date rules can make the calculations less intuitive. For exam purposes, know the basic mechanics and then check whether the question adds special conditions.

Forward and Backward Pass

For simple exam networks:

1. During the forward pass, calculate early dates from project start to finish.
2. During the backward pass, calculate late dates from project finish back to start.
3. Total float is the difference between late and early dates.
4. The critical path usually has the lowest total float.
5. If a required finish date is earlier than the calculated finish, negative float may appear.

Duration and Productivity

If a work quantity and productivity rate are provided:

If crew size affects total production:

Check units carefully. Hours, shifts, calendar days, and workdays are not interchangeable.

Schedule Variance and SPI

Interpret earned value results together with CPM. A value-based schedule variance does not automatically equal a day-for-day delay to project completion.

Lead and Lag

Common Relationship Types

Lags and Leads

A schedule with many constraints, lags, open ends, or missing logic may calculate dates, but it may not be a credible CPM model.

Schedule Quality Review

A schedule can look detailed but still be weak. Quality review focuses on whether the model is logical, complete, maintainable, and useful for control.

Schedule Quality Checklist

Common Schedule Defects

• Open-ended activities with no predecessor or successor.
• Excessive use of start-to-start relationships with large lags.
• Negative lags used to force overlap.
• Constraints used instead of logic.
• Progress entered without remaining duration review.
• Activities with actual dates in the future.
• Forecast dates before the status date.
• Missing long-lead procurement.
• Ignoring testing, turnover, commissioning, or owner approvals.
• Out-of-sequence progress not analyzed.

Percent Complete Types

Earned Value Interpretation

PSP trap: EV schedule variance does not identify the CPM critical path. A project can have favorable SPI while a critical milestone is forecast late.

Leveling vs. Smoothing

Resources, Productivity, and Leveling

Schedules should be achievable with available resources. Resource loading connects work quantities and productivity assumptions to durations.

Resource Concepts

Leveling Decision Rules

A common mistake is assuming more resources always shorten the schedule. In practice, congestion, limited workfaces, rework, supervision limits, and procurement constraints can reduce productivity.

Compression Decision Table

Schedule Compression

Schedule compression attempts to shorten the project duration. It usually increases cost, risk, or coordination burden.

Compression Methods

Compression Exam Trap

If asked for the best compression option, first identify the critical path. Compressing noncritical work does not shorten the project unless it becomes critical or affects a controlling interface.

Risk Formulas

Schedule Risk and Uncertainty

A deterministic CPM schedule uses fixed durations, but real projects contain uncertainty. Schedule risk analysis evaluates the likelihood of different completion outcomes.

Risk Review Points

Risk Traps

• Do not treat CPM completion date as guaranteed.
• Do not bury all contingency in activity durations without transparency.
• Do not ignore near-critical paths.
• Do not assume the longest deterministic path is always the highest-risk path.
• Do not confuse risk response planning with after-the-fact delay analysis.

Change-Control Decision Table

Delay Analysis and Forensic Scheduling

Delay analysis determines how events affected schedule completion or interim milestones. The key issues are usually causation, timing, criticality, concurrency, and entitlement under the applicable contract framework.

Common Delay Analysis Concepts

Delay Analysis Decision Questions

1. What was the controlling critical path before the event?
2. Did the event affect a critical or near-critical activity?
3. Did the event consume float or delay completion?
4. Was there concurrent delay?
5. Are the records contemporaneous and reliable?
6. Did the schedule update accurately reflect actual progress?
7. Was the delay caused by the event, or by unrelated performance issues?
8. What does the contract require for notice, documentation, and analysis?

Avoid jumping from “an event occurred” to “the project was delayed.” The exam often expects you to connect the event to critical path impact.

Good Schedule Narrative Elements

• Data date and reporting period
• Work completed during the period
• Current critical path and near-critical paths
• Major variances from baseline or previous update
• Delays, causes, and responsible mitigation actions
• Changes added, pending, or approved
• Forecast milestone and completion dates
• Risks and recovery actions
• Assumptions affecting the forecast

Reporting and Communication

A scheduler must communicate schedule status clearly to project stakeholders.

Useful Schedule Reports

Good Reporting Practice

• Separate facts, forecasts, assumptions, and recommendations.
• Explain causes of variance, not just date movement.
• Identify critical and near-critical work.
• Show what changed since the last update.
• Make recovery actions specific and accountable.
• Avoid overloading executives with raw activity lists.

Final Readiness Checklist

Before attempting a full mock exam, make sure you can confidently:

• Explain the difference between planning and scheduling.
• Build a logical activity network from scope and WBS.
• Calculate and interpret early dates, late dates, total float, and free float.
• Identify the critical path and near-critical paths.
• Recognize the effect of calendars, lags, constraints, and milestones.
• Update a schedule using actuals, remaining durations, and a status date.
• Compare current schedule forecasts to the baseline.
• Interpret schedule variance without confusing it with CPM delay.
• Evaluate resource loading and leveling impacts.
• Choose appropriate schedule compression methods.
• Understand risk, contingency, and uncertainty in schedule forecasts.
• Analyze delay using causation, criticality, timing, and documentation.

Planning vs. Scheduling

A common exam mistake is to jump directly into CPM calculations without checking whether the schedule has a valid planning basis.

Activity Detail Decision Rules

Float Decision Rules

1. Low float does not automatically mean high importance. It means limited time flexibility.
2. High float does not mean the work can be ignored. Interfaces, resources, and risk still matter.
3. Float is path-based. Delaying one activity can consume float for multiple downstream activities.
4. Negative float requires explanation. It usually points to an imposed date, delay, or recovery need.
5. Critical path can change after progress updates. Do not assume the baseline critical path remains critical.

Conceptual Traps

Calculation Traps

• Forgetting to include lag.
• Ignoring relationship type.
• Treating calendar days as workdays.
• Choosing the path with the most activities instead of the longest duration.
• Calculating free float as if it were total float.
• Missing negative float caused by an imposed finish date.
• Not recalculating after a progress update.
• Rounding productivity or duration too early.
• Comparing baseline and current dates without checking scope changes.

Proper Update Sequence

    flowchart TD
	    A[Set status/data date] --> B[Enter actual starts and finishes]
	    B --> C[Update remaining durations]
	    C --> D[Record percent complete or physical progress]
	    D --> E[Review out-of-sequence work]
	    E --> F[Recalculate schedule]
	    F --> G[Analyze critical and near-critical paths]
	    G --> H[Compare to baseline]
	    H --> I[Report variance and forecast]

Update Quality Checks

Common formulas:

Interpretation Rules

Earned value schedule indicators do not replace CPM analysis. A project can have favorable earned value metrics and still be late if critical path work is delayed.

Schedule Document Review