Total Slack Calculation

[Wiz Kid]

I have a task (Task B) that has a FNLT constraint of a date 04/03/09. It's
Early dates and Late dates are both the same - 04/03/09, but it's Total Slack
= -27 days. This obviously looked incorrect based on the EF and LF dates.

Looked at one of it's driving predecessors (Task A) and noticed that it's
Early Dates were later than its Late Dates by 27 days.

Why does the Total Slack of -27 days occur on Task B ?

 

[Dale Howard [MVP]]

Wiz Kid --

If Task B has a missed Deadline date or a missed inflexible Constraint date
(such as a FNLT or MFO constraint), the software calculates negative Total
Slack. Hope this helps.

 

[Steve House [MVP]]

And adding to Dales response, the negative slack means that you are modeling
a physical impossibility. The forces that are driving when the task will
take place place it's finish date 27 days AFTER your constraint says Project
is permtted to place it in the schedule. It's telling you that if you go
with the plan the way it sits, you'll find that task will finish 27 days
later than it's supposed to and there's nothing you can do to prevent it
without altering the plan. If you're trying to model a mandate that says
you must finish the task by a certain date DO NOT use a FNLT constraint. I
know it seems like that would be right but what you really need is a
deadline, not a constraint. If the objective is to figure out a plan that
will meat your required objectives, you need to let Project freely move
tasks in response to your choices of workflow and resource assigments so it
can tell you if a particular strategy you're considering will be successful.
HTH

 

[Dale Howard [MVP]]

Steve --

Excellent point! Thanks for sharing.

And adding to Dales response, the negative slack means that you are
modeling a physical impossibility. The forces that are driving when the
task will take place place it's finish date 27 days AFTER your constraint
says Project is permtted to place it in the schedule. It's telling you
that if you go with the plan the way it sits, you'll find that task will
finish 27 days later than it's supposed to and there's nothing you can do
to prevent it without altering the plan. If you're trying to model a
mandate that says you must finish the task by a certain date DO NOT use a
FNLT constraint. I know it seems like that would be right but what you
really need is a deadline, not a constraint. If the objective is to
figure out a plan that will meat your required objectives, you need to let
Project freely move tasks in response to your choices of workflow and
resource assigments so it can tell you if a particular strategy you're
considering will be successful.
HTH

--
Steve House [Project MVP]
MS Project Trainer & Consultant
Visit http://project.mvps.org/faqs.htm for the FAQs

I have a task (Task B) that has a FNLT constraint of a date 04/03/09.
It's
Early dates and Late dates are both the same - 04/03/09, but it's Total
Slack
= -27 days. This obviously looked incorrect based on the EF and LF
dates.

Looked at one of it's driving predecessors (Task A) and noticed that it's
Early Dates were later than its Late Dates by 27 days.

Why does the Total Slack of -27 days occur on Task B ?

 

[Steve House [MVP]]

TY - and on re-reading my post I HAVE to stop trying to type and spell
before I've had my second cup of coffee in the morning. Sheesh!

Steve

Steve --

Excellent point! Thanks for sharing.

And adding to Dales response, the negative slack means that you are
modeling a physical impossibility. The forces that are driving when the
task will take place place it's finish date 27 days AFTER your constraint
says Project is permtted to place it in the schedule. It's telling you
that if you go with the plan the way it sits, you'll find that task will
finish 27 days later than it's supposed to and there's nothing you can do
to prevent it without altering the plan. If you're trying to model a
mandate that says you must finish the task by a certain date DO NOT use a
FNLT constraint. I know it seems like that would be right but what you
really need is a deadline, not a constraint. If the objective is to
figure out a plan that will meat your required objectives, you need to
let Project freely move tasks in response to your choices of workflow and
resource assigments so it can tell you if a particular strategy you're
considering will be successful.
HTH

--
Steve House [Project MVP]
MS Project Trainer & Consultant
Visit http://project.mvps.org/faqs.htm for the FAQs

I have a task (Task B) that has a FNLT constraint of a date 04/03/09.
It's
Early dates and Late dates are both the same - 04/03/09, but it's Total
Slack
= -27 days. This obviously looked incorrect based on the EF and LF
dates.

Looked at one of it's driving predecessors (Task A) and noticed that
it's
Early Dates were later than its Late Dates by 27 days.

Why does the Total Slack of -27 days occur on Task B ?