A network diagram is the basic
features of the network planning. It is a diagram which represents all the
events and activities in a sequence with their inter-relationships and
inter-dependencies. The arrow diagram is a visual of a network diagram, where every
activity is represented by an arrows. Arrows diagrams are useful for providing
information and making decisions in large projects.
Example
Calculate the earliest start
time, earliest finish time, latest start time and latest finish time for the
following network diagram show below time given for all activities is in days.
Solution :
- The EST is calculated by starting from the event 1 i.e. Activity 'A' and giving it a time 0 (EST). EST for event No. 1 = 0
- The EST of activity B = 0 + duration of = 0 + 10 = 10 days
- The EST of activity ‘D’ = EST of B + duration of ‘B’
= 10 + 20
= 30 days
- The EST of activity C = 0 + duration of A
= 0 + 10
= 10 days
- EST of activity event No. 4 is maximum of
- EST for event No. 2 + duration on of activity ‘C’ = 10 +25 = 35 days
- And EST for event No.3 + duration of D = 30+25 = 55 days i.e. EST for event No. 4 is 55 days. These EST for all events are shown in the figure in the left side of the time box. The latest finish time can be calculated as follows.
- LFT for event No. 4 = 55 days
- LFT for event No. 3 = LFT for event No. 4 – duration of activity D
= 55 – 25
= 30 days
- LFT for event No. 2 is minimum of LFT for event No. 3 – duration of activity ‘B’ = 30 – 20 = 10 days.
- LFT for event No. 4 – duration of activity ‘C’ = 55 – 25 = 30 days. Therefore LFT for event No. 2 is 10 days.
- LFT for event No. 1 = LFT for event No. 2 – duration of activity ‘A’
= 10 – 10
= 0 days
|
Activity
|
Duration
D
|
EST
|
LST (LFT – D)
|
EFT (EST + D)
|
LFT
|
Total Float
|
Remarks
|
|
A
|
10
|
0
|
0
|
10
|
10
|
10
|
Critical
|
|
B
|
20
|
10
|
10
|
30
|
30
|
30
|
Critical
|
|
C
|
25
|
10
|
30
|
35
|
55
|
55
|
|
|
D
|
25
|
30
|
30
|
55
|
55
|
55
|
Critical
|
Total Float = (LST – EST) OR
(LFT – EFT)
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