The Critical Path Method
CPM Basics
Let’s begin by exploring what CPM is, it’s history, and the big picture.
What is CPM?
CPM stands for the Critical Path Method and is used for calculating when a set of activities will start and finish based on their durations and their relationships between each other. They’re made up of:
- Activities
- Relationships
Is that it?
Yes! A schedule then is simply a network of Activities and Relationships, or nodes & links, respectively. You might be thinking, “ A network? I just have a list of tasks, how is that a network?”.
You can have both. Just like your friends, you have a list of them, but like a network, there’s a set that you see together all the time, or a friend that doesn’t want to be around another friend, or a friend who will only come by if certain conditions are met.
In this schedule network, there is a path or series of activities that is longer than any other path. This is the critical path!
Why CPM is used in construction
Construction is one of the most demanding types of projects. The number of participants, constraints, resources, and moving parts is unparalleled.
Luckily, CPM is here to help manage these moving parts. It assists in answering questions such as:
- If a task is delayed by a few weeks, how does that affect our overall finish date?
- Which areas or tasks need the most attention?
- Where is my priority?
- Am I late?
- How much flexibility does this task have?
- When is the earliest this task can start?
- When is the latest this task can start?
- Why can’t I start this task now?
Sure, if your project is small enough, you might be able to calculate the answers to these questions in your head.
In reality, a significant amount of math is needed to find the answers to these questions.
Yes, it’s just math!
Wait, computers are good at math!