Schedule Reliability and Buffers

Project schedules tend toward tardiness, but what can be done to make schedules more reliably on time? Schedule buffer similar to a cost contingency helps projects become more reliable.

Project plans are generally more optimistic than reality. Reasons for this disconnect are that project plans do not consider: inefficiencies in the handover of tasks between resources, workplace congestion, coordination among contributors, and the multitasking of critical resources. One would think that not accounting for these delay effects would be counter balanced by contributors padding their estimates. But this is not the case. Once a duration is entered in the project plan (whether conservative or optimistic) it becomes subject to all the drag effects of Parkinson’s Law and procrastination.

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Why You Should Avoid Mandatory Activity Constraints

If you just cannot get your schedule to match an important finish milestone deadline you may be tempted to go “thermonuclear” by inserting a Mandatory Finish constraint on the milestone. You’ll definitely get your important finish date this way, but there will be collateral damage to your schedule. Let’s explore this.

If you want a child to stay away from a stove top burner you could simply tell the child ‘do not touch’. A more indirect approach is to tell them about the stove, and in doing so provide them knowledge that warns them to stay away. The later approach is our intent today in explaining mandatory constraints. We are telling you how mandatory constraints work not so you will haphazardly use them, but so that you will know enough to be cautious and even wary of their use.

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Creating a Believable Schedule

Defining activities is an important part of scheduling. Part of the complexity of the project is determined by the number of activities required to complete that project. When it comes to the size and/or placement of the activities, several control factors should be considered. Once the project has been broken down into unique definable elements of work, the duration of these elements must be accurately estimated. Accurate definition of activities and their durations creates all the elements necessary for a believable schedule.

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Why won’t my activities Start/End on the correct day?

From primaverablog.in

There have been times when activities in Primavera don’t Start or End on correct dates despite the math saying otherwise . There are several reasons that can cause this to happen, lets look at them in this post.

1) Out of Sequence Activities – These are activities that have started before the predecessor activities are completed. These activities are created when you using “Retained Logic” as your scheduling preference. This creates non-working periods and this can cause the activity to be pushed out of the normal calculated dates. You can check which activities are being pushed Out of Sequence by checking. You can choose “Progress Override” to schedule and correct these dates or change relationships for these activities. For a better explanation on these option check this blog post Scheduling Options – Progressing Activities .

2) The activity calendar contains non-work time that is pushing the finish date out.

3) Resource Leveling – “Level resources during scheduling” option should be unchecked in “Schedule Options” when you schedule the project.

4) Multiple calendars – If you are using multiple calendars and the number of working hours do not match the Time Period settings under Admin Preferences then the activities might end on a different time of the day.

5) Constraints - If an Activity has an “As late as possible” constraint. The As late as possible constraint allows an activity to start or finish as late as possible without delaying its successors. This constraint sets the early dates as late as possible without affecting successor activities. Even if the activity is started, the Finish date can be pushed later in time if positive total float exists when the As late as possible constraint is applied. This will make the Finish date appear to be later than it would be based on the remaining duration.

6) Project has Activities with Actual Dates > Data Date – To check if any of your activities has this problem you need to go to Tools, Schedule open schedule log. In the schedule log, you need to check and see if any activities are listed in the Activities with Actual Dates > Data Date section. If yes, then you can either remove the actual dates, or move the data date after the actual dates.

Time Unit configuration

The definition and configuration of time unit on P6 has been a matter of misunderstanding. This a blog post about it with a concepts clarification and a configuration preview example.

Although we can define the Time units in Hours, Days, Weeks, Months or Years but P6 stores the time unit values in HOURS in the database. Then it can be displayed in Days, Weeks etc. The conversion between different units of time is carried out based on the conversion defined in Admin > Admin Preferences > Time Periods Tab. There we can define Hours/Day, Hours/Week and Hours/Year. This can be defined only by administrators. There is a checkbox “Use assigned calendar to specify the number of work hours for each time period”. It is advised to keep this checkbox checked if the working hours/day in an individual calendar is not same to that defined in Admin Preferences. Because if the Original Duration for an activity is defined in hours and the time units are displayed in “Days” or “Months” then there might be some inaccurate display. Let us understand this by an example;

Let us set 8 hours/day in the Admin > Admin Preferences > Time Periods Tab. The checkbox “Use assigned calendar to specify the number of work hours for each time period” is unchecked. Now define a calendar and keep the Working Hours per day = 12 (contrary to what we defined in Admin Preferences). Now insert an activity. Go to Edit > User Preferences > Time Units Tab, and Change the Duration Format to Hour. Enter the activity duration as 41 hours (i.e. we defined an activity which has duration of 41 hours and the calendar assigned has 12 hours/day as working hours). Now change the duration format to Days. By calculation, we should have 41/12 = 3.42 days. But we can see that P6 has calculated it as 5.13 days (i.e. 41/8=5.13). It means that P6 is still using the conversion defined in the Admin Preferences which is wrong because in calendar we have 12 working hours/day. This problem can be avoided if checkbox “Use assigned calendar to specify the number of work hours for each time period” is kept checked in Admin Preferences.