Critical Path RRS feed

  • Question

  • Hi,

    I am working on a MP schedule for a project and i have scheduled the program from the project start date. The types of relationships used among the tasks are a mixtures of milestones, constraints, FS, SF, FF & SS relations with lags etc. Also, have set critical path as zero days. Questions :

    a. Is it correct or appropriate to use SF relationships if scheduling a project from start date?

    b. Can i say the end or completion date of the project is always on critical path? Since there is no way to indicate to the program the finish date of the project (as i am scheduling from project start).

    c. I have some tasks with total slack of zero, i have looked in & out of the schedule but could not find a way to increase the total slack. I am trying to reduce some activities with critical path but to no avail. Can anyone have a look at my schedule?

    Thank you

    Tuesday, February 25, 2014 5:23 AM

All replies

  • Hi WK88,

    a. the most usual and common (and I'd say easy) way to schedule a project plan from the start day is to use FS (finish to start) relationship. Indeed this is the usual dependency between tasks in a project : the successor will start when the predecessor will finish, eventually adding a lag (+ or -). See more details about SF relationaship in this thraed:

    b. indeed the lastest task/milestone (meaning the task with the latest finish date) of your project plan will always be critical since if you delay the latest task, it will delay the project finish date, thus the total slck is equal to 0 and the task is critical.

    c. here are a few links for helping you on the critical path.

    Note that the most obvious way to increase the total slack will be to shorten the duration of the task. for example by adding resources or decreasing the work (see this link about fast-tracking your project: Check also for deadlines that could make tasks as critical.

    Hope this helps.

    Guillaume Rouyre - MBA, MCP, MCTS

    Tuesday, February 25, 2014 2:16 PM
  • WK88 --

    Allow me to render some opinions to answer your questions:

    1. Yes, you can use Start-to-Finish (SF) dependencies in a project scheduled from a Start date.  My question for you would be whether SF accurately describes the relationship between the two tasks.
    2. The Finish date of the project is calculated by Microsoft Project as the Finish date of the lastest finishing task. By default, the latest finishing task will always be on the Critical path, until that task is completed.
    3. One way to increase Total Slack for a task is to add a Start No Earlier Than constraint to the task's immediate Successor task and to set the Constraint Date of the Successor task to start later than the Successor task's current Start date.  For example, the Successor task currently has a Start date of 03/18/14.  Apply a Start No Earlier Than constraint to this task with a Constraint Date of 3/20/14.  For this task's immediate Predecessor task, you will now see a Total Slack value of 2 days.

    Just some thoughts.  I hope some others in this forum will give you their opinions as well.  Hope this helps.

    Dale A. Howard [MVP]

    Tuesday, February 25, 2014 2:20 PM
  • Allow me to render yet more opinions!

    1. Yes, but limited only. For example if you run a 1 day workshop, having a task called prepare for workshop preceding it with a SF link is very appropriate as it most accurately reflects what needs to happen.
    2. The last task is always critical as Dale and Guillaume said. However I refine this by adding a milestone called Project closure at the bottom of my schedule. I set a start no earlier date constraint and a date after the previous last task to finish. No all tasks except this new milestone are non-critical.
      I now add Deadline dates to all tasks that have specific deadlines from the business plan, or set by the Project Sponsor/Project Manager. This is what I call the Real critical path as the critical path now only shows tasks that are critical for delivering key milestones.
    3. The only way to add total slack to a task is to reduce its duration and or the duration of finish dates of its predecessors until a parallel chain of tasks becomes critical and your milestone gets some Total slack.

    Rod Gill
    Author of the one and only Project VBA Book

    Tuesday, February 25, 2014 8:49 PM
  • Dear All,

    Thanks for the advise. I will look through the links to find a suitable solution.

    Other questions in my mind...

    a) When I put a link of FS between 2 activities, i often get the start of the successor having the same finish date of the predecessor. So there is some overlap between the 2 activities. Is it because of the calendar being used? I have all of my task using the same calendar at the project information center. Do i need to change the calendar type under the task information for each and everyone of the tasks eventhough if i have indicated the type of calender in project information.

    b) Do i need to click F9 (like in P3) everytime i have changed something in the schedule? Sometimes the total slack will change after i clicking F9, from -10 to 0, so which is the correct figure since i have mark auto-schedule in scheduling option at the very beginning. Such changes are confusing, can it be a program issue (i am on MP 2007).

    Back to c) of my initial queries, i have input those tasks with zero total float and have them complete later but to my surprise, they have not changed the final completion date of the project. In general, they should not be considered as a critical task but why is their total slack indicated as zero!
    • Edited by WK88 Wednesday, February 26, 2014 3:21 AM
    Wednesday, February 26, 2014 2:24 AM
  • Hi WK88,

    a) When you use the defaut FS relationship, the start date of the successor will most of the time be the same than the finish date of the predecessor, unless (the list might not be exhaustive):

    • you have a constraint on the start date of the successor such as start no earlier than
    • you inserted a lag in the relationship
    • the predecessor ends just before the week-end, so the successor will start on the next monday
    • any exceptions in the calendar (project calendar or resource calendar if a resource is assigned to the task
    • you perform any resources levelling that might have delayed some tasks

    Concerning the calendar, tasks will be scheduled based on the project calendar thus you don't have to specify a task calendar, unless you need to (night shifts for a specific task for example)

    b) hitting F9 in MS Project 2007 might be sometimes helpful to refresh custom fields with formulas, or relationships. My advice would be to press after updating your project, just to be sure that everything has been recalculated.

    c) please send me you file (guillaumeDOTrouyreATgcosiDOTcom, replace caps) or post a screenshot mentionning which tasks are causing you troubles, I'll try to have a look.

    Hoep this helps.

    Guillaume Rouyre - MBA, MCP, MCTS

    Wednesday, February 26, 2014 1:56 PM