AACE PSP cheat sheet

A project schedule is a model of planned work over time; the plan defines scope, WBS, activities, logic, durations, and resources before scheduling begins.

WBS decomposition rule: each work package should be assignable to a single accountable owner and estimable for cost and duration; 8-80 hour rule is a common work-package sizing heuristic.

Activity duration estimating methods: analogous (top-down, historical similarity), parametric (unit-rate × quantity), and bottom-up (roll up detailed estimates); three-point PERT expected duration = (O + 4M + P) / 6.

PERT standard deviation = (P - O) / 6; variance = ((P - O) / 6)^2; path variance is the sum of activity variances along the path.

Dependency types: FS (finish-to-start), SS (start-to-start), FF (finish-to-finish), SF (start-to-finish); each may carry lag (positive) or lead (negative).

Calendar assignment drives duration math: a 5-day duration on a 5-day/week calendar spans 7 calendar days; resource calendars can differ from the project calendar.

Milestones are zero-duration events marking contractual or decision points; a start milestone or finish milestone is used to anchor open-ended logic.

Rolling wave planning: detail near-term work fully and leave far-term work at summary level, refining as the project advances.

CPM forward pass: ES = max(EF of predecessors + lag); EF = ES + duration. Backward pass: LF = min(LS of successors - lag); LS = LF - duration.

Total float (TF) = LS - ES = LF - EF; free float (FF) = min(ES of successors) - EF. Float is a property of the path, not just the activity.

The critical path is the longest continuous path through the network; its total float equals zero (or the minimum value if a constraint sets a negative/positive project float).

Negative total float indicates a schedule that cannot meet a imposed finish date; positive float indicates slack against the imposed date.

A constraint (e.g., start-no-earlier-than, finish-no-later-than) overrides logic; a hard constraint can break the CPM float calculation and should be minimized.

Resource leveling changes start/finish dates to resolve over-allocation and may extend the critical path; resource smoothing (time-limited) adjusts within float without moving the finish date.

Lags model wait time (e.g., cure concrete); leads model overlap. Excessive lags hide logic and are a common audit finding.

Schedule types by purpose: baseline schedule (approved plan), update schedule (progressed), recovery schedule (to regain lost time), and what-if/target schedule.

Progress update: record actual start/finish and remaining duration; percent complete by duration = (actual duration) / (actual + remaining duration), not by cost or units unless defined.

Out-of-sequence progress (actual started before a predecessor finished) must be resolved - typically by adding a logic link or a retained/soft constraint - before the update is valid.

Baseline vs. update comparison yields schedule variance; finish variance = current forecast finish - baseline finish (negative = ahead).

Data date (status date) is the point in time to which progress is recorded; all work before it is actual, work after it is forecast.

Schedule performance index (time) = earned schedule / actual time (ES/AT); SPI(t) < 1.0 indicates behind schedule.

Earned schedule: ES is the date on the baseline when planned value equals current earned value; it improves on classic SPI which converges to 1.0 at project end.

Change control: any logic, duration, or calendar change after baseline approval requires documented approval and a re-baselined or revised schedule.

Schedule health checks: no open-ended activities (except start/finish milestones), no negative lags, minimal constraints, no excessive total float, valid critical path.

Critical path method identifies the driving path; near-critical paths (float below a threshold, e.g., <= 10 days) should be reported alongside the critical path.

Float analysis / total float distribution: report count of activities by float band; a schedule with most activities at zero float is fragile.

Schedule risk analysis uses Monte Carlo simulation over duration uncertainty (three-point estimates) to produce a probabilistic finish date (e.g., P50, P80) and a contingency buffer.

Joint confidence level (JCL) expresses the probability that a project finishes on or under a given cost and schedule target simultaneously.

Driving path in a risk-adjusted schedule is the chain of activities whose duration uncertainty most influences the probabilistic finish date.

Schedule compression: crashing adds resources/cost to shorten critical activities; fast-tracking overlaps activities (parallel) and increases risk.

Reporting: S-curve (planned vs. earned vs. actual), Gantt with critical path highlighted, milestone trend chart, and look-ahead (2-6 week) schedules for execution.

A schedule narrative documents basis of schedule: assumptions, calendars, constraints, float, critical path, and major risks - required for a defensible baseline.