2. TIMINGS OF ACTIVITIES
The earliest time start time (EST) of each node is determined by the forward pass (FP) through the network. Then add duration (DUR) of the activity to EST, which gives earliest finish time (EFT) for that node. The EST for the following activity is the EFT of the previous activity. If there are number of activities merging into the single node then, the EST for that activity will be the preceding activity with greatest EFT.
Appendix 1 – simple calculations
When the project is to be completed by the given time frame, it’s crucial to know how long an activity can occur. This can be calculated by the backward pass (BP) exactly opposite to the FP. Latest start time (LST) for any activity is determined by subtracting DUR from Latest finish time (LFT) for that activity. The LFT of the final activity is the total project time.
Appendix 2 – simple calculations
TOTAL FLOAT (TF)
When earliest start time is subtracted from latest start time, the difference obtained is the float. Float indicates how long an activity can be delayed without affecting the entire project. “..Float is a quantity that denotes the priority of a task, the highest priorities naturally beign given to those task which have least float. This proposition allows project management attention and actions to be directed to the most critical activities.” (Stevens, M. Project Management Pathways (2002) p. 16)
Appendix 3 – simple calculations
3. PROJECT DURATION AND THE CRITICAL PATH
Project duration is the nearest time by which the project can be accomplished. The EFT/LFT of the last node of the network diagram shows the duration of the project. Vobien Ltd has the project duration of 50 days.
The path from start to the finishing of the project such that delay in any task of the path could result in the delay of the project is the critical path (CP). Moreover the series of activities with zero slack is called the CP. CP determines the earliest time the project can be finished. According to Field and Keller (1998), “Critical Path is normally easily spotted as they pass through nodes with the same earliest and latest times.”
The Critical Path for the Vobien Project is – A,B,C,F,G,K,L,M,N,O,Q,R
4. EARLIEST COMPLETION DATE OF PROJECT
If the project commences on Monday 15th July 2013, the earliest date it can be concluded working 5 days a week and project duration of 50 days will give us 10 work weeks.
Since the project is started on 15th July 2013, with 50 working days, the earliest completion date will be Friday 20th September 2013.
Appendix 4 –Calendar 5. EFFECTS ON THE DURATION OF THE PROJECT
A. activity E is not on the CP; hence will have no effect on the duration of the project if it`s delayed by 1 day
B. activity P is not on the CP; hence will have no effect on the project if it`s delayed 2 days.
C. if activity Q is completed 1 day early, then the FP completion date of the project will be 1 day earlier as activity Q is on CP.
6. LIMITATIONS OF NETWORK DIAGRAMS
a. Sometimes the network diagrams are hard to follow when they possess too many lines and intersections.
b. This is not a good communication method because it`s tough to understand information such as total float and to update the diagram especially for big projects with frequent changes.
c. “Calculations are not quite as obvious with such a convention and this may cause little confusion.” (Field, M. and Keller, L (1998) p. 198 They are in days so it`s difficult to calculate finishing date as weekends and holidays are not considered.
d. Sometimes network diagrams become focus of too much attention while other issues may be main cause of problems. E.g.: management; labour relations.
e. Network diagrams gives only overview on the duration of each activity and on overall project completion time, they do not allow resource planning and reference to milestones.
