Introduction to CPM / PERT Techniques

CPM/PERT or Network Analysis is the technique is at times called, developed with two parallel streams, one military and the other industrial.

CPM (Critical Path Method) was the invention of M.R.Walker of E.I.Du Pont de Nemours & Co. and J.E.Kelly of Remington Rand, circa 1957. The calculation was created for the UNIVAC-I computer. The first test was prepared in 1958, when CPM was applied to the development of a new chemical plant. In March 1959, the technique was applied to maintenance shut-down at the Du Pont works in Louisville, Kentucky. Unproductive time was decreaed from 125 to 93 hours.

PERT (Project Evaluation and Review Technique) was introduced in 1958 for the POLARIS missile program by the Program Evaluation Branch of the Special Projects office of the U.S.Navy, assisted by the Lockheed Missile Systems division and the Consultant firm of Booz-Allen & Hamilton. The calculations were maintained so that they could be carried out on the IBM Naval Ordinance Research Computer (NORC) at Dahlgren, Virginia.

The methods are fundamentally network-oriented techniques using the similar principle. PERT and CPM are essentially time-oriented methods in sense that they both move for determination of a time schedule for the project. The important difference between two approaches is that the time approximation for the dissimilar activities in CPM was implicit to be deterministic whereas in PERT these are explained probabilistically. These techniques are known as project scheduling techniques.

In CPM activities are revealed as a network of precedence relationships taking use of activity-on-node network construction

-        Deterministic activity times

-        Single estimate of activity time

USED IN:  Production management - for the jobs of recurring in nature where the activity time estimates can be forecasted with considerable certainty because of existence of past experience.

In PERT, activities are revealed as a network of precedence relationships taking use of activity-on-arrow network construction

-        Probabilistic activity times

-        Multiple time estimates

USED IN: Project management - for non-recurring jobs (research and development work), where the time and cost approximates tend to be somewhat doubtful. This technique utilizes probabilistic time estimates.

Advantages of PERT/CPM

l  Helpful at various stages of project management

l  Mathematically easy

l  Provide critical path and slack time

l  Give project documentation

l  Helpful in monitoring and controlling costs

Demerits of PERT/CPM

l  Fairly defined, independent and stable activities

l  Precise precedence relationships

l  More stress on critical paths

Applications of CPM / PERT 

These methods have been used in a wide range of problems in industries and have found approval even in government organizations. These comprise

• Building of a dam or a canal system in an area
• Building of a building or highway
• Space flight
• Preservation or overhaul of airplanes or oil refinery
• Cost control of a project with the help of PERT / COST
• Creating a prototype of a machine
• Creation of supersonic planes