Making a Pizza Using a Critical Path Method Example
Baking a pizza from scratch is a simple project that can be used to illustrate the steps of the Critical Path Method. In the following example, there is a clear sequence of events that must happen in the right order and the duration of each activity can be estimated. This allows the project manager, in this case the cook, to be able to predict the time that dinner will be on the table.
List and Sequence the Activities
The first step when beginning the CPA is to list the activities for the project. In this pizza example, the steps would be as follows: list ingredients, gather and purchase ingredients, mix ingredients for the dough, let dough rest, roll dough, grate cheese, heat tomato sauce, cover dough with sauce and cheese, pre-heat the oven, bake the pizza in the oven, serve and eat. The steps of grating the cheese and heating the tomato sauce do not need to be part of a particular point in the sequence, however they do need to be completed before the step of placing them on the dough. Pre-heating the oven can also be started at any point before the pizza is ready to be placed in the oven.
Estimate Time for Each Activity
Next the project manager must determine how long each activity will take. For the pizza example, each task is assigned an estimation of the shortest and longest time to completion, represented in the following list by the numbers in parenthesis: list ingredients (5-10), gather and purchase ingredients (20-60), mix ingredients for the dough (10-20), let dough rest (60), roll dough (5-10), grate cheese (5-10), heat tomato sauce (2-5), cover dough with sauce and cheese (2-5), pre-heat the oven (5-10), bake the pizza in the oven (20-30), serve and eat (20-30).
Create the Model
In CPA analysis, a diagram would be created placing each of the tasks in sequence. As mentioned earlier, the tasks of grating cheese, heating sauce and pre-heating the oven are not part of the critical path sequence, rather these activities could be categorized as sub-critical, and shown in parallel on the model. In an Activity-on-Node diagram, the activities would be shown as boxes or circles with arrows representing the relationships between them. The short and long estimated time of each task is noted, as well as the elapsed duration of the project after each task is completed.
Determine the Critical Path and Float
In making this pizza from start to finish, the longest duration of time would be the combination of the critical tasks in the timeline. Thus the total critical path timeline would be equal to a range between 142 minutes at the minimum to 225 minutes at maximum. The float time for the tasks on the parallel timeline would be 10 minutes, the activities' longest duration. These sub-critical tasks can be performed at the same time as the critical path tasks, and can even be performed two or three at a time, such as heating the oven while grating the cheese.
Begin Project and Monitor Adherence
After creation of the diagrams and project time estimations, the project is ready to begin. The pizza maker starts with making the ingredients list and proceeds to gathering and shopping for ingredients. If the tasks are delayed or interrupted, for example if the cook receives an important phone call that requires attention, the timeline will be changed. In order to meet the deadline and have the pizza prepared on time, the cook must add resources like additional help in the kitchen, or adapt the tasks for example by purchasing ready-made dough.
Even from this simple pizza making illustration it is clear that a project manager must carefully plan and monitor the activities in order to meet deadlines. When unexpected delays and obstacles arise, the manager must use additional resources to ensure the project is completed, and on time.