Event
It is the start of completion
of a task. It is represented by a circle and does not consume time and
resources.
Activity
An activity is the actual
performance of a task. It consumes time and resources such as manpower,
materials etc. and it is represented by the line and arrow.
For example,
Start Machine installation : An
event
Machine installation : Activity
Completion of machine
installations : An event
Successor Event
Successor event is an event
which immediately follows another event.
Predecessor Event
Predecessor event is an event
which takes place immediately before a particular event.
Earliest Expected Time (Te)
It is the earliest expected
time of the project and is equal to the sum of the expected times of all the
activities, along with the longest path at the project.
Latest Allowable Time (TL)
It is the largest possible time
that event can take without causing delay in the final completion date.
TL for an event = Total expected time for the end
of an event of a project from the longest path – Total expected time for the
event under consideration from the longest path.
Slack (TL – Te)
Slack is the difference between
the latest allowable time (TL) and the Earliest Expected Time (Te).
It is the span of time available for the performance of an activity without any
delay in the completion date of the project. This value of slack indicates how
critical that event is and how much stress given on that activity.
Critical Path
This is a path on the network
along which no slippage is allowed. In this path, slack is either negative or
zero.
Example
Show the earliest and the
latest expected time on the following network and indicate the Critical Path on
it.
Solution
The Earliest and the Latest
times are shown on the network given in the figure below in this network, the
Critical Path will be the path along the events 1, 2, 5 and 6 because on this
whole path Te = TL i.e. slack is always equal to zero.
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