🏗️ Construction Scheduler Field Guide

The 4 relationship types

Lags and leads

A lag is a built-in waiting period on a relationship. "FS + 3 days" means: A finishes, wait 3 days, then B can start. Classic example: concrete needs cure time before you strip forms.

A lead (negative lag, like "FS − 2") means the successor starts before the predecessor finishes. Schedule checkers hate leads because they hide overlap that should be modeled with an SS relationship instead. Rule of thumb: zero leads, and use lags sparingly with a reason you can say out loud (like cure time). Never use a lag just to push a date — that's called "hiding logic."

Open ends, constraints, and other logic vocabulary

• Open end: an activity missing a predecessor or a successor. Except for the first and last activities, everything should have both. Open-ended activities can "float" to weird dates and break the critical path calculation.
• Constraint: a pinned date forced onto an activity (like "Must Finish By Dec 15"). A hard constraint overrides logic and can create fake dates; a soft constraint (like "Start No Earlier Than") bends with logic. Use constraints only for real contract dates, and as few as possible — the schedule should be driven by logic, not pins.
• Redundant logic: a tie that's already implied by other ties (A→B→C plus a direct A→C). Harmless to the math, but clutters the schedule.
• Out-of-sequence progress: when the field does work in a different order than your logic said. The software has to decide how to handle it (see "Retained Logic" in the P6 tab). It's a sign your logic needs a conversation with the superintendent.
• Driving relationship: among all of an activity's predecessors, the one that actually controls when it can start. The chain of driving relationships from start to finish is the longest path.

🧮 Relationship date calculator

Pick a relationship type and see when the successor can start. Uses simple "project day" numbers (Day 1 = first workday).

Master formula table

Day-number convention: Day 1 is the first workday and durations are in workdays. P6 does the same math internally with calendars and dates.

🧮 1. Duration from quantity take-off

This is the exact skill your job posting asks for: "prepares quantity take-offs and incorporates the production analysis into the schedule."

🧮 2. Three-point (PERT) duration estimate

PERT = Program Evaluation and Review Technique. When nobody's sure how long something takes, get three guesses and weight the middle one.

🧮 3. Float (slack) calculator

Enter the four CPM dates for one activity (as day numbers) and get its float. Float = wiggle room.

🧮 4. Remaining duration from progress

The pro move at update time: don't ask "what percent are you?" — ask "how much is LEFT and how fast are you going?"

🧮 5. Workdays ↔ calendar days

Durations are in workdays, but people think in calendar time. A "20-day" activity on a 5-day week takes about 4 real weeks.

🧮 6. Earned Value quick check (EVM)

EVM = Earned Value Management. It compares the value of work planned, work done, and money spent. Your posting mentions validating the cost forecast against the schedule — this is that conversation.

Try it: a 10-activity building project

Change any duration below and hit Run CPM. The tool runs a real forward and backward pass — exactly what P6 does when you press F9. Critical activities turn red. Try making "Underground Utilities" 15 days instead of 8 and watch the critical path move.

How the passes work (the part interviewers ask about)

1. Forward pass — start at the beginning. Each activity's Early Start (ES) = the day after its latest-finishing predecessor. Early Finish (EF) = ES + duration − 1. When an activity has several predecessors, it must wait for all of them — so it takes the latest EF.
2. Backward pass — start at the end. Each activity's Late Finish (LF) = the day before its earliest-starting successor. Late Start (LS) = LF − duration + 1. With several successors, take the earliest LS.
3. Total Float (TF) = LS − ES. Zero float = critical. Negative float = you're already late (the schedule can't hit a required date).

Version timeline, 2015 → today

P6 concepts you must be able to talk about

The DCMA 14-point health check

🧮 DCMA health check calculator

Type in the counts from your schedule (P6 filters or an export to Excel get you these numbers) and get instant pass/fail on the measurable checks.

Activity counts

Relationship counts

Execution & critical path

Outside software & processes for checking schedules

Interactive Planning Session (IPS) — also called a pull plan

A working meeting where the people who will DO the work build the sequence together, usually with sticky notes on a wall (or a digital board). "Pull" planning means you start from a milestone (like "Building dried-in Nov 1") and work backward, each trade saying what they need finished before they can start.

1. Prep (you): pick the milestone and window (usually 6–12 weeks), invite every trade involved, print the current schedule for that area, bring sticky notes color-coded by trade.
2. Set the target: put the milestone on the right end of the wall.
3. Pull backward: the last trade posts what they need done before they can start; the trade before them does the same; repeat until you reach today.
4. Negotiate the collisions: two trades want the same room the same week — this is where the meeting earns its keep. The super referees; you capture.
5. Test durations: ask each trade "what crew size does that duration assume?" Write it down — that's your production-rate backup.
6. You translate: after the meeting, turn the wall into activities and logic in P6, then send it back to the room for a "did I capture it right?" check.

The rhythm of a project (typical cadence)

The 3-week look-ahead (some companies use 4 or 6) is your most-read product: a simple list of what's happening this week and the next two, by area and trade. Field people may never open P6 — but they read the look-ahead every week. Make it clean, accurate, and boring in the best way.

Getting good status from foremen and subs

People calibrate over time: some foremen are optimists ("two days" means five), some sandbag. Track promises vs. actuals in your notebook — after a month you'll know everyone's conversion rate. Never use it to embarrass anyone; use it to forecast better.

The paper trail that drives schedules

• RFI (Request For Information) — a formal question to the designer ("the drawings conflict — which is right?"). Open RFIs block work; track the ones sitting on critical activities.
• Submittal — documents/samples a sub sends for approval before building (shop drawings, product data). Long approval + fabrication lead times belong IN the schedule as procurement activities.
• Change Order (CO) — an approved change to scope, price, or time. If it adds work, it adds activities — and maybe a Time Impact Analysis.
• Long-lead items — equipment that takes months to arrive (switchgear, elevators, air handlers). Rookie schedulers model the install and forget the 6-month wait before it. Model: submit → approve → fabricate → deliver → install.
• NTP (Notice To Proceed), Substantial Completion, LDs (Liquidated Damages — daily money owed for finishing late): the contract dates your whole schedule serves. Read the contract's schedule section on day one.

Writing the monthly schedule narrative

Every formal update comes with a short written story. Standard skeleton: 1) current data date and forecast completion vs. baseline; 2) progress this period (what started/finished); 3) critical path description in plain sentences; 4) changes since last update and why; 5) risks and delays, with who owns each; 6) look-ahead of major work next period. Two pages, no drama, no surprises that weren't already communicated in person.