Critical path and resource levelling

0:00Sara: Welcome to Project Management Exam Prep.

0:02This episode is about the critical path and resource levelling.

0:06It asks which work sets the end date, and whether the people are there when needed.

0:12Leo: You will learn to draw the network, find the critical path, read the float,

0:17and fit the plan to your people. We finish with a calculation drill,

0:21so keep a pen ready.

0:23Sara: Let us start with the three lenses. What does IPMA® say?

0:27Leo: IPMA®, the International Project Management Association, sets out its standard in

0:32the Individual Competence Baseline, the ICB4.

0:36Its element on time asks you to calculate the critical path and level the resources

0:41of a given plan. Scarce people, it notes, can change that path.

0:47Its element on resources links people to the schedule.

0:51Sara: And PMI®?

0:52Leo: PMI®, the Project Management Institute, publishes the PMBOK® Guide,

0:58its guide to the project management body of knowledge.

1:01Its eighth edition lists the critical path method, leveling and smoothing among

1:06its tools. The outline of PMI®'s Project Management Professional exam,

1:11the PMP®, covers them in two tasks: plan and manage the schedule,

1:16and plan and manage resources.

1:19Sara: And APM?

1:21Leo: APM, the Association for Project Management, publishes the APM Body of Knowledge.

1:27It calls the method critical path analysis: software does the calculation,

1:32but you must be able to check it. The syllabus of APM's Project Management Qualification,

1:37the PMQ, asks how smoothing differs from levelling.

1:41Sara: Where do the words differ?

1:43Leo: In two places. First, the name: the critical path method for PMI®,

1:49critical path analysis for APM, and network analysis in the ICB4.

1:55Second, smoothing. For PMI®, it moves work only within float.

2:00APM also lets it add or remove people on an activity, so that the date holds.

2:05Sara: What is the core, whichever exam you take?

2:08Leo: Three ideas. One: draw the logic, with a box for each activity and an arrow for

2:15each dependency. That is activity on node.

2:19Most arrows are finish-to-start: one activity ends, then the next begins.

2:25Other kinds let work overlap; this network needs none.

2:29Sara: Two?

2:31Leo: Every path must be finished, so the longest one sets the end date.

2:36That is the critical path. Other activities have float, room to slip.

2:41Sara: And three?

2:43Leo: People are a limit too: a week that needs more people than you have cannot run as

2:48drawn.

2:48Sara: And in agile work?

2:51Leo: A timebox fixes the time and the team, and the scope flexes, so there is little

2:57to level inside it. But hybrid plans keep a network above the timeboxes,

3:02for fixed dates, suppliers and hand-offs between teams.

3:07Sara: Now the method, on a free model sheet in the description.

3:11Leo: James Kelley and Morgan Walker published the critical path method in nineteen fifty-nine.

3:16Take a city team's last ten weeks before go-live, with four people.

3:21A, the sign-off of the rules, takes two weeks and two people.

3:26B, C and D follow it. B, configure: four weeks, two people.

3:32C, migrate the data: three weeks, two people.

3:36D, the service-desk guide: two weeks, one person.

3:40E, the test, follows B and C: two weeks, four people.

3:44F, training, follows D and E: two weeks, three people.

3:50Sara: Now the forward pass.

3:52Leo: It gives each activity's early start and early finish.

3:56Count from zero, so a start of two means the end of week two.

4:01Add the duration to get the early finish.

4:04An activity starts only when all its predecessors are done, so where arrows meet,

4:09take the largest finish. A goes from zero to two.

4:14B, C and D start at two. B ends at six, C at five, and D at four.

4:20E waits for B and C: six to eight. F waits for D and E: eight to ten.

4:26Ten weeks.

4:28Sara: And the backward pass?

4:30Leo: It works back from the end. Subtract the duration to get the late start.

4:35An activity must end before its first successor must start, so where arrows split,

4:40take the smallest start. F must start by eight, and E by six.

4:46D must end by eight, for training, so it must start by six.

4:50B and C must end by six, for the test. So B must start by two,

4:55and C by three. A must end by two.

4:59Sara: Where is the critical path?

5:01Leo: First, total float: how long an activity can slip without moving the end date.

5:06It is late start minus early start. A, B, E and F have none.

5:12C has one week: three minus two. D has four: six minus two.

5:18The chain with no float, A, B, E and F, is the critical path:

5:22ten weeks. The path through C takes nine: it is near-critical,

5:27so watch it too.

5:29Sara: And free float?

5:31Leo: How long an activity can slip before the next one must start later:

5:34the next early start, minus its own early finish.

5:39For C, six minus five: one week. Here both kinds are equal.

5:44They differ when two activities with float follow each other.

5:48If the first slips, the second starts later, but the end date holds.

5:52Sara: Now the people.

5:54Leo: Add up the people week by week in the early-start plan: that is the resource histogram.

6:00In weeks three and four, B, C and D run together.

6:03They need five people, one more than the team has.

6:07Sara: What do I do?

6:08Leo: First, ask for a fifth person for those two weeks.

6:12If you cannot, try resource smoothing: the end date stays, and work moves only within

6:18float. Here it fails. Between weeks three and eight, only one week has room.

6:26D needs two weeks in a row, so some week always needs five.

6:31Resource levelling keeps the limit of four, and lets the date move.

6:36When people are short, the least float goes first.

6:40So D waits for C's people until the end of week five.

6:44At the end of week six, the test needs four, but D still holds one.

6:49So the test waits a week, and go-live moves to the end of week eleven.

6:54Sara: How does this change between Mid-level and Senior?

6:58Leo: First, the two levels. They are this series' own labels.

7:02Mid-level means leading moderately complex projects, the level of IPMA® Level C and

7:08PMI®'s PMP® exam. Senior means leading complex projects and people,

7:15the level of IPMA® Level B and of APM's chartered status, Chartered Project Professional.

7:22At Mid-level, you calculate and act on your own plan.

7:25Take Parking Permits Online, a city project that moves resident parking permits

7:30online in eight months. The project manager, Anna, finds that levelling its last

7:36ten weeks costs a week. So she asks her steering group: a fifth person for two weeks,

7:42or go-live a week later, nearer January, when most residents renew?

7:47Sara: And at Senior level?

7:49Leo: You set the scheduling rules for others.

7:52Take One City Account, a thirty-month city project that brings fourteen online services

7:57under one login, led by Anna some years later.

8:02Six integration specialists serve all the city's projects, so people,

8:06not only logic, set Anna's dates. The steering board agrees her rule.

8:11Work tied to the national login's quarterly releases keeps its date and buys extra

8:16people. Other work is levelled to the city's allocation.

8:20Sara: Now the drill. A city team has ten weeks and four people before a new online service

8:26goes live. Its plan is the worked example's network, on screen again.

8:32Now C's estimate drops from three weeks to two.

8:36What is the critical path, and can you stay at four people without moving go-live?

8:41Leo: Pause and write your answer. You have forty-five seconds.

9:30Sara: First, the network.

9:32Leo: C now ends at four. The test still starts at six, after B.

9:38So C may start as late as four. Its total float is four minus two:

9:42two weeks. The critical path is still A, B, E and F: ten weeks.

9:49Sara: And the people?

9:51Leo: Weeks three and four still need five: B, C and D.

9:55But weeks five and six now need only B's two.

9:59So smooth: move D two weeks later, into weeks five and six.

10:04No week needs more than four, go-live holds, and D keeps two weeks of float.

10:09Moving C also fits, but it leaves the migration no float.

10:13Sara: What lifts that to Senior?

10:15Leo: The date has almost no tolerance, so keep C's spare weeks as a visible buffer for

10:20the migration. Agree D's new weeks with the guide writers' line manager.

10:25And set a rule: who may spend float, and who must be told.

10:29Sara: How do the exams ask this?

10:32Leo: IPMA®'s exams ask for open answers. IPMA®'s certification also includes an interview,

10:37where assessors ask about your own projects: note one plan you levelled.

10:43The PMP® exam uses scenarios, and questions built on a case study or a chart:

10:48practise reading a network. APM's PMQ asks for short written answers,

10:53such as how smoothing differs from levelling.

10:56Sara: Let us recap.

10:58Leo: One. Draw the logic: boxes for activities, arrows for dependencies.

11:04Sara: Two. Forward, take the largest finish. Backward, take the smallest start.

11:10Leo: Three. Total float is late start minus early start.

11:13None means critical.

11:15Sara: Four. The histogram adds up the people per week.

11:19Leo: And five. Ask for people first. Smoothing keeps the date; levelling keeps the limit.

11:24Sara: The three model sheets and the study handout are free in the description.

11:29Next time: estimation.