Arrow Diagramming Method(ADM)
Arrow diagramming method (ADM) is a network diagramming technique in which activities are represented by arrows. ADM is also known as the Activity-On-Arrow (AOA) method. It has been used long time to determine the critical path and identify resource problems and feasible solutions when the approximate duration and resource requirement of all the activities of network diagram are known.
There are two main elements of the Arrow Diagramming Method(ADM) which are arrows and nodes. One arrow represents one activity to be performed. The tail of the arrow is the start of the activity, the head of the arrow is the end of the activity and the length of the arrow is often scaled to be proportional to the duration of the activity.
For better understanding lets analyze the schema below.
The circles numbered 1, 2, 3 and 4 are the nodes of this network system. They are the definable achievement in the project. Nodes have neither duration nor resource. Activities A,B,C,D are represented by the arrows. Each activity has duration and allocated resource. A dummy task which is not a real activity is added to represent a dependency between tasks. It can be used to separate tasks or to keep the sequence correct. Duration of a dummy task is often zero.
The Arrow Diagram was a common visible and practical network diagramming method used in the past which was developed after the bar chart.
As a traditional project management toolkit Arrow Diagramming Method(ADM)’ s popularity is has fallen away because of the introduction of software solutions that can calculate the critical path of a project schedule easily and automatically.
 CPM in Construction – A Manual for General Contractors(Copyright 1965 by the Associated General Contractors of America)
See Also: Precedence Diagramming Method Example