Re: Buffer or lag periods

LOL - John and I are on opposite sides of the philosophical fence on this one - I am strongly opposed to ever using fixed duration scheduling except in very specific circumstances. Fixed duration is simply a workaround to impose a set of schedule dates on the project, trying to sever the relationship between work and duration. The assumption is that if the task will take longer than you want it to, making the resource work harder will solve the problem and make the task fit into the time you want to allow for it. But it won't work - in a well managed firm resources are always working as hard as they're ever going to work so if it's going to take him 3 days to polish 100 fids, it will take him 3 days no matter what your schedule calls for, whether you've budgeted 10 days or 1 day. The task might be a test that must run for exactly 4 hours, no more and no less, for its results to be valid so something like that could be a candidate to be entered as a fixed duration task but that's about it. In my opinion, a manager does not decide how long a task *ought* to take. Instead, a manager seeks to *discover* how long a task will *need* to take to get the required result. Scheduling becomes an act of discovery, not an imposition of will.

Frankly, I don't see why you're building these buffers into the task at all - If your best estimate is that it should take 3 days to get the fids ready to polish, coordinate with the resource to verify that your estimate is reasonably accurate and to get a buy-in on your expectations from him, and then schedule it that way. Build the schedule on the assumption that it WILL take 3 days and you can schedule the next task in line to start on day 4. What you're doing by putting on buffers is saying "I think we'll be ready to go on day 4 but I'm not going to promise it'll start until day 6 so that in the event the first task takes a little longer than planned I don't ever have to go to my boss with the news that we're going to run later than I'd originaly expected." Basically you're trying CYA to insure that reality is never worse that first estimates. But the end result is going to be a "worst case" schedule than has the project scheduled to last longer than it really could take to get it done. And human psychology being what it is, Joe Resource will say to himself "I could get 'er done in 3 days but the boss has given me 6 so why break a sweat?" and the old saw about the work expanding to fill the time allotted for it will come true.

Baselines are not targets to be engraved in granite - they are a record of your best-guess schedule estimates preserved in order to measure progress.

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


"SR" <SR@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message news:72E1D835-DB0A-4C3C-8BF9-47E26DEB777E@xxxxxxxxxxxxxxxx
Thanks Steve. Out of the three solution yu provided, i can only apply one
(reducing the resource usage). I tried this option before. It used to take a
lot of time to calculate this and for a project with around 1000 tasks, it is
very time cosuming. That is why I started using Lag days. But now I realize
may be the resource usage is a better option. but do let me know if you have
any other alternatives. I cann't increase the effort as i track the cost and
my budget will go up.

I used to adjust the usage % by hit & trial, keeping in mind the date i am
targeting. my effort hrs are not always whole numbers nor multiple of 8. May
be any alternate simple way to do this will also help.

--
sr


"Steve House" wrote:

As you've discovered, lags aren't the same as a buffer. A lag time of,
say, 3 day between tasks means that there MUST be a 3 day delay between
the completion of the first task and the start of the second. For
example, perhaps you'll always need 3 days of curing time between
pouring concrete in the first task before starting to paint it in the
second task. No matter what date task 1 ends, task 2 should not start
until 3 days later.

Frankly, the best way to use the buffers is to include them in the
task's duration estimate. You say you don't know duration but you can
estimate it. If you think work will require 40 man-hours and you knw
you can have your resource full time, the duration will probably be 40
hours as well (5 days). So to add a 25% buffer set the duration to 50
hours. Or if you don't want to disturb the work estimate, set the
duration to 50 hours and assign the resource at 75% - work will be 40
hours.
--
Steve House
MS Project MVP
Visit http://www.mvps.org/project/faqs.htm for the FAQs



"SR" <SR@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:5DE79B5A-6975-4173-9C29-3AE5069422B1@xxxxxxxxxxxxxxxx
> Thank John but may be i was not clear earlier.
>
> I do not at all touch the start & finish date. that is why to adjust
the
> date i put this lag.
> lets say I have Task A - efft hrs 16 hrs & Task B - eff hr - 32 but
the dur
> i don't know and hv one resource (not 100%) actual %ge not available.
>
> If i simply schd B after A with Start-Finish, it will finish in 6 days
with
> no lag. But then since the resource is not available 100%, A is not
going to
> finish in 2 days. So what i do I keep "TaskAFS+5 days" in predecessor
col.
> that gives me 5 days and i can maitain my baseline dates. but if the
takes 4
> days and when i enter the actual finish date, it automatically adds
another 5
> ds for Task B to start. I have to manually go and reduce the lag days
to 2 so
> that the next task start can start on time.
>
> What I am asking here is, is there any way to have this buffer so that
i
> don't deviate from baseline dates and also keep some extra room for
each task
>
>
>
> -- > sr
>
>
> "John" wrote:
>
> > In article <94E7E50F-EA84-457E-9883-DD8490F2E0AE@xxxxxxxxxxxxx>,
> > SR <SR@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > > Hi,
> > >
> > > I am working in a functional unit projs where resources work in
multiple
> > > projs. My prob is, when i create my plan, i only know the
estimated hrs for
> > > each task and the % of resource availability. So it is really
difficult for
> > > me to schedule the exact dates that a particular task is going to
finish. The
> > > way I am doing is, take resource as 100% available and keep some
buffer days
> > > (lag) for the next task to start. this i do by adding lags for the
next task.
> > > e.g - if a 16 effort hrs task starts on 7/3. my schd will have an
end date
> > > for this task 7/4 and with a lag of 5 days, next task will start
7/12.
> > > Problem here is - when the task finishes on 7/10 with no effort
variance, the
> > > start date for next task automatically set to 7/18 for 5 lag days.
I then
> > > have to remove this lag to start on 7/11.
> > >
> > > Saying that - cann't put date contraints as actually do not have
any
> > > - duration available for the proj is always much
higher
> > > than estmated hours.
> > > - should not vary from the baseline dates for
main tasks as
> > > the resource are blocked for the baseline dates for other
functional groups.
> > >
> > > Does any one has any idea how to fix this problem or a better
solution to
> > > schedule the task.
> >
> > SR,
> > Your scenario is very typical - you have an estimate for the number
of
> > hours required to do a task and you know who you want to work on it.
The
> > problem I see in what you have described is that you appear to be
> > "forcing" the schedule, perhaps even doing something you should not
and
> > that is to directly entering start and finish dates for tasks.
> >
> > The whole reason for using Project is to allow it to schedule your
> > project based on some basic inputs - task description, estimated
> > duration, schedule logic (links), estimated work, and resource
> > assignments. Is your plan going to be perfect? No, it never is.
Remember
> > most of the data is estimated so the initial schedule is a best
guess
> > estimate of how the plan will unfold. As the plan is executed, it is
> > updated and modified as necessary to reflect newer information.
> >
> > It is also not clear if you understand the difference between
duration
> > time and work time. Duration is the time during which a task will be
> > completed. It is expressed in working time as the difference between
the
> > Start and Finish fields. Work on the other hand is the amount of
time
> > one or more resources will expend actually performing the task. If a
> > single resource is assigned at 100%, then duration and work will be
the
> > same. However it is also very common to have a duration time that is
> > longer than the work time. For example, painting a room may take 5
days
> > but the estimated work to paint the room may only be 30 hours.
> >
> > It is very rare that you will have all the resources you want/need
to
> > complete your plan. It is also very rare that there is actually
enough
> > time to execute the plan as you would like. Those are the realities
of
> > the business world. Your job is to create the most reasonable but
> > realistic plan with the assets available to you. If you truly can't
get
> > there from here, then you need to make your case to your management
for
> > more time and/or resources.
> >
> > John
> > Project MVP
> >




.

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