Method (CPM) are scheduling techniques used to plan, schedule, budget and control the many activities associated with projects. Projects are usually very large, complex, custom products that consist of many interrelated activities to be performed either concurrently or sequentially. The planning horizon for PERT/CPM
typically extends beyond the six-month time frame of traditional short-range planning used in the other production processes.
Utilizing PERT/CPM involves breaking the total project down into many different individual activities with identifiable time
Each activity must be accomplished as part of the
total work to be done. Custom products (made to customer specification) are produced with a project process; therefore, the customer's desired completion date is the focal point for scheduling. time to begin work on the project is determined by working backward from the customer’s desired completion date. Project The
managers must coordinate each of the activities so the project can be completed at the desired date and with minimal costs. The PERT/CPM schedule allows for converting the project plans
into an operating timetable; thus, provides direction for managing the day-to-day activities of projects. Although application of both PERT and CPM follow the same steps and use network diagrams to schedule and control projects, the primary difference between these two techniques is that PERT is probabilistic where CPM is deterministic. The terms PERT and
CPM will be used together or interchangeably in this paper to present the basic principles behind the application of these techniques. In addition, deterministic activity times in this
paper will be used to illustrate the techniques.
A SIMPLE EXAMPLE A simple exercise (scheduling a student's morning) is used here to illustrate the principles of applying PERT/CPM to a set of interrelated activities. A student has several activities
that must be performed either simultaneously or sequentially before he/she attends a 9:30 class. The activities have been
identified as individual activities to be done prior to attending class. The desired completion time for these
activities is 9:30, otherwise the student will be late for class. A list of activities that must be performed prior to
class and the time required to do the activities are as follows:
# A. B. C. D. E. F. G.
Activity Wake-up & get out of bed Shower Dress Prepare Breakfast Eat Breakfast Brush Teeth Transportation to Class
Time Required = = = = = = = 10 10 10 20 15 5 40 minutes minutes minutes minutes minutes minutes minutes
Assuming these tasks must be performed sequentially according to the activity number presented in the list, a network diagram illustrating the relationships among the activities can be developed (see Figure 1).
A 1 2
ACTIVITIES PRIOR TO 9:30 CLASS
If the student scheduling the activities begins at some point in time (zero) and moves through the path of activities in sequence (in this example there is only one path; however, complex projects may have hundreds of paths), the student will find that the shortest time required to complete all the activities prior to class is:
Since these activities take 110 minutes to complete, the student must begin the first activity at 7:20 in order to arrive at the 9:30 class on time. Each activity's start and end times can be
determined and then used by the student to control his/her ontime arrival for the 9:30 class. PERT/CPM requires a network diagram of all the activities graphically interrelated showing the precedence...