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Introduction

A network diagram is also known as a PERT Chart (Program Evaluation and Review Technique). PERT charts were developed in the 1950s under contract to the United States Department of Defence. They are used to organise and coordinate tasks within a project and can be done by hand or by using a software package such as Microsoft Project.

There are two different ways these diagrams can be presented.

Method 1: Activity on the node

This chart has tasks positioned inside activity boxes which are linked by arrows. One pathway through the chart starts with 'site work' which is followed by 'construct garage slab', then 'construct concrete driveway slab' and finally 'clean up'. The other pathway begins with 'obtain materials' which has two branches leading to 'construct garage slab' and 'prefab wall panels'. This path then leads to 'erect wall' which further branches to the three tasks 'erect trusses', 'erect trusses' and 'install sliding windows' and 'install door'. 'Erect trusses' then branches to 'install roof'. All three paths then finish at the final box 'paint'.

In this diagram the activities are written inside the boxes and are linked by arrows. These arrows may or may not have the number of days to complete the task written on them.

Method 2: Activity on the arrow

This diagram contains the same information as the previous chart, but tasks are written above the arrows between numbered circles. The first circle is labelled 'S' for start, and the subsequent circles are numbered in intervals of five. The final circle is 'F' for finish.

In this diagram the actual activities to be carried out are written on the arrows. The activities are set out numerically which allows for sub-events to happen in between. Gaps are left between the numbers in the nodes (circles) to allow the sub-events to fit in. On large building sites these numbers may count in 20s or 50s or even 100s, whilst on smaller jobs these could be actual days within the construction program.

The more common method in use is method 2 - activity on the arrow. Each of the numbered nodes (the circles) represents an activity which has been completed while each arrow represents an activity that has taken place.