Q: What is a PERT chart?
A. A network diagram
B. A precedence diagram
C. A project management planning tool
D. An evaluation technique developed by the U.S. Navy for use in the Polaris submarine missile program
E. All of the above
If you guessed “E,” you’re absolutely correct! But now you might be asking: “Why does one chart have so many different names? What do the Navy and project management have in common? And did you say missiles?”
We did say missiles. As it turns out, this half-century old naval technique is more applicable to present-day project management than you might think.
To learn how PERT charts are used today for project planning, we interviewed Dr. Dan Patterson, CEO and founder of risk advisory group PMFocus, and Kevin Archbold, consulting manager for project management consulting firm Key Consulting.
Here’s what we’ll cover:
What Is a PERT Chart?
A schematic of the project schedule.
PERT, or project/program evaluation review technique, accounts for inevitable changes that occur in a project’s schedule that impact the project finish.
The technique was initially developed by the Navy in the 1950s for the Polaris submarine project. Today, PERT charts are used by teams across industries looking to plan and execute their projects more effectively.
Simply stated, a PERT chart is a graphic representation of a project schedule.
The schedule is shown as a network diagram most commonly illustrated with “nodes,” representing important tasks or milestones, and “vectors,” or directional lines, illustrating the sequence of the tasks.
A network diagram shows the sequence of tasks and milestones, but it also illustrates how those tasks and milestones are prioritized—i.e., their precedence. This is why PERT charts are often referred to as “network diagrams” or “precedence diagrams.”
A true PERT chart involves a 3-point estimation technique, which assigns three possible duration estimates to each task:
- Most likely
Estimating duration this way allows managers to calculate a more realistic project schedule.
How Are PERT Charts Used in Project Management?
As a data visualization tool.
PERT charts help project teams visualize the order of tasks, milestones and phases within a project. Illustrating the project schedule makes it easy to identify tasks as one of two types:
- Dependent, or sequential tasks
- Non-dependent, or concurrent tasks
This allows managers to coordinate work across teams and departments more effectively.
“[PERT charts] do an excellent job of showing when work is to be executed and how that work relates to other areas of scope in the project.”
DR. DAN PATTERSON, CEO AND FOUNDER OF PMFOCUS
“Add to this the ability to color code nodes in a PERT chart to represent additional metadata such as cost or resources and your PERT chart then becomes even more powerful.”
PERT charts are often used in conjunction with another popular data visualization tool: Gantt charts. Gantt charts also depict the project schedule, but instead of a network diagram, Gantt charts show the schedule as a horizontal bar chart across a calendar.
Key Consulting’s Archbold states that: “A Gantt chart should be developed from the network diagram. … A Gantt chart derived from a network diagram is much easier to maintain and is more accurate.”
Archbold explains that network diagrams are the core of the project schedule. While Gantt charts are useful for ensuring teams stick to a schedule, PERT charts should be used to calculate a realistic timetable before the project even begins.
Once a project is underway, managers use the PERT chart to monitor the accuracy of the project schedule. They do this by swapping out forecasted start dates with actual start dates. If the difference exceeds the given float, updates to subsequent tasks and the project end-date are reflected in the Gantt chart.
“As project progress is collected, the network diagram is used to recalculate the schedule. Each week the [project manager] should be able to forecast whether the project end-date can be met.”
KEVIN ARCHBOLD, CONSULTING MANAGER FOR KEY CONSULTING
What Are Some Best Practices for Creating PERT Charts?
Keep it simple.
One of the challenges with PERT charts is that they show a lot of detailed information for each task including:
- Task name
- Planned and actual start
- Estimated duration
- Name of responsible person
This level of detail can quickly get out of hand when dealing with long, complex projects that have a high volume of tasks with multiple phases and milestones.
According to Patterson, one way to combat this issue is to keep the PERT chart relevant to the audience:
“All projects can be represented as hierarchies. A project can be broken down into multiple levels, and so a best practice technique should be [to] report your overall project at a level that doesn’t demand more than say 20 nodes.”
DR. DAN PATTERSON, CEO AND FOUNDER OF PMFOCUS
Patterson advises using a “break-out” PERT chart with the tasks and milestones relevant to specific teams and/or departments—e.g., a chart that shows only those tasks and milestones pertinent to Engineering and another for Marketing. This keeps the PERT chart from becoming overly complicated.
How Is PERT Chart Software Beneficial to Project Managers?
Automate processes, reduce manual errors.
Project managers can create PERT charts using a variety of methods. The most common are manually drawing them or using a spreadsheet tool, such as Excel.
Let’s take a closer look:
|Drag-and-drop functionality||Managers can easily create PERT charts by dragging and dropping tasks to different points on a schedule and make updates as required.|
|Automatic calculations||Recalculates changes in duration estimates when “planned start” differs from “actual start” and updates items that are affected as a result.|
|Integration with other solutions||Visualization tools that integrate with project management software allow for greater visibility and understanding of project variables such as: timeline constraints, resource availability/utility and potential risk areas.|
|Pre-built templates||Templates and automatic formatting not only simplify creation of PERT chart but also look more professional.|
|Version control||Makes it easy to share charts with project team members and stakeholders. Especially when using cloud-based tools, updates are reflected in real-time helping keep teams stay apprised of any changes.|
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