The above curve is called the learning curve . All these points should be taken into account while planning resources .

4. Construction the network : In the critical path method , network is a directed graph . A directed graph is a structure formulated by nodes , which are tied by directed arrow .
   Let be the set of nodes , and
   be the directed arrow
   The graph of the activity network is represented mathematically by the symbol [N,P] .
   There are two logic diagramming formats used in CPM -
   1. Activity on the arrow .(AOA)
   
   
   2. Activity on the node . (AON)
      
   1. Activity on the arrow (AOA) : In this format , activity is denoted by the arrow and nodes merely serve as connecting points for the activity . We often require to use activity with zero time called dummy activity to retain the logic and grammatical rules of the network . The network is constructed on the logic that an activity leaving a node cannot begin until all the activity heading into that node have been completed . This diagramming format has widely been used .