PERT is a technique that organizes a project's tasks by their order and durations to plan and manage the overall schedule.
List the tasks
Set the predecessors
Estimate the days
Draw it, find the total time
Draw the order and days as an arrow diagram and find the total duration.
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For each task, you decide which tasks must finish before it (its predecessors) and how many days it needs. Drawing the result as an arrow diagram (アローダイアグラム) shows the total duration and which tasks can run in parallel. After the plan is made, it is also used to manage the schedule by revising it to match actual progress.
AnalogyIt is like planning a house move. You cannot carry anything out until it is packed, but you can file your change-of-address paperwork while you pack. Once you write down the order and the days, you can see how long the whole move will take.
How to rememberIt stands for Program Evaluation and Review Technique. The word Review in the name reminds you that it is a method for revising the plan as work moves forward.
Exam points
ExamOnce you know each task's predecessors and duration, you can calculate the minimum number of days needed to finish all the work.
ExamDurations need not be in days. The same approach of order and time applies to procedures measured in seconds or minutes.
An arrow diagram (アローダイアグラム) shows tasks as arrows and the breaks between tasks as circles called nodes, setting out the order of tasks and their durations.
Change a duration and the critical path and the total are recalculated at once.
Total duration: 10 days
Critical path: A → B → E
Each arrow stands for one task, its direction shows the order, and the number beside it gives the duration. Nodes mark where tasks start and end. An arrow that carries no actual work and only expresses an ordering is a dummy activity, drawn as a dotted line with a duration of 0.
How to rememberThe name comes from the English word arrow. True to the name, tasks are drawn as the arrows, not as the circles.
Exam points
ExamWhen several arrows lead into a node, a task leaving that node cannot start until every incoming task is finished.
Mix-upAn arrow diagram (アローダイアグラム) shows task order and schedule. A diagram that sorts the factors affecting quality into the shape of a fish skeleton is a cause-and-effect diagram (特性要因図), which is something else.
Critical path analysis (クリティカルパス分析) finds, among the paths from start to finish on an arrow diagram, the one with the largest total of days (the critical path), and uses it to find the shortest possible overall duration.
List the paths
Total days per path
Pick the largest total
That total = shortest overall time
The whole job takes at least 10 days, and tasks C and D have room to slip without delaying it.
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A project is not complete until the tasks on every path are done, so the days on the longest path become the overall duration. If a task on the critical path slips, completion of the whole project slips by the same number of days, so these tasks get close attention. Every other task has some days it can be delayed without lengthening the overall duration, called its float.
AnalogyWhen several people split up the cooking and start at the same time, dinner is not fully on the table until the most time-consuming dish is ready. That dish's steps decide when the whole meal is done.
How to rememberCritical here means decisive. A delay on this path decides the completion date, which the word itself reminds you of.
Exam points
ExamA task that is not on the critical path (クリティカルパス) can take more days without lengthening the overall duration, up to the difference between the critical path and the longest path that runs through that task.
ExamIf other work can proceed in parallel during a waiting period, treat that parallel work as a separate path; the overall time is set by the longest path.
Mix-upThe critical path (クリティカルパス) is the path with the largest total of days, not the smallest.
A matrix diagram (マトリックス図) lists two sets of elements as rows and columns and marks each cell where they cross with a symbol for whether and how strongly they relate, organizing how the two sets correspond.
Requirement / Design item
Screen size
Device weight
Battery capacity
Easy-to-read text
◎
－
－
Easy to carry
○
◎
○
Long battery life
○
－
◎
Because one set of elements runs down the row headings and the other across the column headings, you can survey every combination without missing any. Each cell gets a symbol such as ◎ (strong relationship), ○ (related), or － (unrelated), which helps you spot strongly related and unrelated combinations. Like the arrow diagram, it is counted among the seven new QC tools.
AnalogyIt is like a duty roster. With names down the side and chores across the top, circling the cells each person covers shows at a glance who does what and which chores have no one assigned.
How to rememberMatrix is the same word as in mathematics. Just as an entry in a matrix is identified by its row and column, the position of a cell itself stands for one combination.
Exam points
Mix-upA chart that lines up bars from the most frequent item down and overlays a cumulative-percentage line is a Pareto chart (パレート図), which differs from a matrix diagram (マトリックス図) that organizes how rows and columns correspond.
Examining combinations such as requirements and functions
Key points
PERT is a technique for planning and managing a schedule from task order and durations, and its plan is drawn as an arrow diagram.
In an arrow diagram, arrows are tasks and nodes are the breaks between them; a dotted arrow that only expresses an ordering and takes 0 days is a dummy activity.
Of the paths from start to finish, the one with the largest total of days is the critical path, and that total is the shortest possible overall duration.
A delay on the critical path delays the whole project, while every other task has some float.
A matrix diagram lists two sets of elements as rows and columns and organizes how they correspond at each intersection.