Free Slack

[SwapnaK]

Can anyone please help me understand how to calculate Free Slack. Is it
the same as calculating Slack for tasks with Predecessors or is it
something else?

 

[salgud]

Can anyone please help me understand how to calculate Free Slack. Is it
the same as calculating Slack for tasks with Predecessors or is it
something else?

There are 2 kinds of slack (float). One is Total Slack and is the
difference between the Late Start and Early Start of the task. It is the
amount of time a task can slip without slipping the end date of the
project. Free Slack (Float) is a little harder to describe. It is the
amount of time a task can slip without effecting any other task. It is
calculated by taking the ES of it's earliest sucessor and subtracting the
Early Finish of the task your caluculating the FS for.
The ramifications of FS are one of the CPM scheduling subtleties of which
most schedulers are unaware, but it is very useful to know. It's definition
is easy to find in the literature. It's meaning is more obscure and harder
to find much about in the literature.
Hope this helps in your world.

 

[Steve House]

I'm not sure what you mean by your question ... tasks have free and total
slack regardless of whether they have predecessors or not and they are
calculated the same way regardless. But for the schedule to be done
properly there should be not tasks without predecessors anyway.

Basic rules of proper scheduling...
All projects have at least a Start Milestone and a Finish Milestone
All activities within the project have at least one predecessor and one
successor.
If a task has no other activity before it, the start milestone is its
predecessor
If a task has no other activity following it, the finish milestone is
its successor.
In other words, there may be multiple chains of events running from the
start milestone to the finish milestone and all tasks, without exception,
lie on at least one of them.

HTH