2. 2) Determination of Timing of Activities and Total Float A network diagram is the display of the activities and the relationships among those activities that are logically arranged. To determine the timing of activities, we need to use the activity-on-node (AON) method, also known as the Precedence Diagram Method (PDM). To understand this better, we first need to define the following: (EST) Early start Time is the earliest time the activity can begin. (LST) Late start Time is the latest time the activity can begin and still allow the project to be completed on time.
EFT) Early finish Time is the earliest time the activity can end. (LET) Late finish Time is the latest time the activity can end and still allow the project to be completed on time Diagram A: Activity-on-the-node diagram Timing of activities in the network diagram is determined by the following calculations for each node as shown in diagram A. Using the forward pass method, the EST + Duration = EFT. Similarly, using the backward pass method, the LFT- Duration = LST. To determine if an activity is critical or not, the EST and LST or the EFT and LFT has to be equal.
The difference between LST and EST or LFT and EFT is called Float or Slack. In conclusion, Total Float, TF = LST-EST = LET-EFT AS defined by Burke (2003) “Float the measure of an activity’s flexibility, quantifying how many working days the activity can be delayed before it will extend the completion date of the project, or any target finish dates. ” Another words, float is the amount of time an activity can slip without any delay in the project finish date. Free float is the amount of time an activity can slip without any delay in the early start of any activity that immediately follows.