“How Do You Know When to Use a Constraint or Lag?”

QUESTION

“P6 lets me add constraints and lags to activity relationships. How do you know when to use a constraint or lag on an activity and which one is best for each situation?”

ANSWER

This question seems to be a favourite in our P6 training courses. Not all relationships are the same when it comes to project planning. External and internal factors can impose challenges that project managers have to deal with ASAP! There is no specific rule that says when to use a constraint or lag on an activity, but based on what each does we can make an educated assumption.

First, let’s talk about constraints.

CONSTRAINTS

Constraints are set in P6 to specify a date or a point in time when an activity can begin or end. Constraints can also be imposed on the entire project. Constraints can be thought of as “rules” – they are concrete in the schedule. Constraints are imposed by external forces, like a delay in delivery of materials or a date a stakeholder requires the project to be finished. Constraints are best used on milestones but can also be used on individual activities. A rule of thumb is that the less constraints you use the better.

You can assign two constraints to an activity if it can only be completed in a specific time frame. For example, if a site is only available from Feb 1 to Feb 14 for a 5 day activity, you could assign a “Start On or After” constraint to Feb 1 and a “Finish On or Before” constraint to Feb 14 to have the activity completed between these dates.

Constraints can ignore network logic, if needed, to meet the requirements you set. In this way, constraints can affect your project schedule negatively if you do not complete predecessor activities on-time.

Overview of Constraints:

• Constraints are used to set dates in the schedule that must be met.
• Constraints directly affect the activity they are set to, and then indirectly affect the predecessor and successor activities.
• Use constraints on milestone activities to meet deadlines.
• Constraints Lare “rules” that cannot be changed.
• Do not assign too many constraints, or network logic can be ignored.

Lags, on the other hand, do not set specific dates. Instead, you can set a delay or a lead time for a predecessor or successor activity. If you enter a positive number, you will delay the successor activity by the number of days specified. In contrast, if you enter a negative number (lead), you will reduce the length of time between the activity and its predecessor.

Lags are usually imposed by internal forces. For example, a lag could be due to drying time required for concrete laid. These are forces that are due to the nature of the activity, not by an external force. In this example, you could add a 10 day lag to wait for the paint or concrete to dry completely and to begin the next activity. The date of the next activity will change depending on when the predecessor activity is finished.

Overview of Lags:

• Lags are used to set delays or lead time between two activities.
• Lags affect the relationship between two activities (predecessor and successor).
• Apply lags to any activity type, but usually task dependent or resource dependent.
• Lags are calculated using the predecessor’s calendar.
• Lags are used when an internal force causes an activity to be delayed.
• Lags are more “controllable” within the schedule.

CONCLUSION

Both lags and constraints should be applied with caution because of the effect that it can have on the schedule. The main difference is that constraints should be used when there is an external force, whereas lags should be used when there is an internal force affecting the activity. As a best practice, always add a note in the activity Notebook tab to indicate why you are adding the constraint or lag to an activity so that other P6 users do not change anything without prior knowledge.

Primavera Functions That Project Managers Must Know

Oracle Primavera helps to make your project management responsibilities easier and more efficient. However, understanding all of the tips and tricks in Primavera functions does not necessarily mean that you will be productive.

Instead, you need to know how to perform certain, specific actions and functions, and this list will help you get on your way towards a more successful, productive schedule.

Read the rest here

From Innovative Management Solutions

To Shorten The Critical Path

Project Managers are typically under great pressure to complete the project in as little time as possible. It is therefore imperative that project managers become familiar with the basic techniques to shorten the critical path and the many different ways to do this.

Read the post on Ten Six

The Negatives of Negative Lag

Are you looking for ways to fast track your schedule? Fast tracking or “crashing the schedule” can employ various methods, but typically takes activities that are scheduled in series and performs all or some of their duration in parallel to shorten the project’s planned or remaining lifecycle.

If you want to shorten your schedule by fast tracking then you most likely are considering the use of lags or negative lags, the latter otherwise known as ‘leads’.

Read the rest on Tensix Blog

Measuring Project Progress: 6 Methods You Should Know

By Reshma Sadhu

Accurately measuring the progress of a project is always a challenge. There are many factors to account for in an progress update – type of measurement, accuracy of the data, frequency of the collect and the system of record are all important factor in accurate progress measurements.

And software packages like Primavera P6 don’t always help us out. Sure there a 3 choices for Percent Complete Types, but how to we decide which one works best and under which conditions?

Inaccurate progress will foil your ability to spot early warning signs of trouble ahead, so to avoid that, here are 6 common methods for measuring project progress that will help you best measure performance and work completion. The methods below are summarized from “Project Control: Integrating Cost and Schedule in Construction,” by Wayne Del Pico.

 

1. Units Completed

The Units Completed lends itself well to tracking tasks that are done repeatedly, where each iteration can easily measured. Usually a task that is done repeatedly tends to take about the same amount of time, resources and effort, so tracking the units completed works well here. A simple example could be installing standard light fixtures. Each fixture takes roughly the same amount of time; if we had 100 fixtures to install then we can simply count the units installed. In this case there’s no subjective experience-based judgement involved.

 

2. Incremental Milestones

Also known as the ‘steps’ method, the incremental milestones method is predominantly used for cost accounts that involve subtasks that need to be completed in an orderly fashion. An example of this technique is the forming and placing of a concrete foundation wall. Laying the foundation wall on footings, erecting inside wall panels and brace, setting horizontal and vertical rebar in formwork and so forth needs to be done in sequence to complete the task appropriately.

So how do you calculate this data? The calculation is built on each single item step and the budgeted amount of time (labor hours) that is needed to complete the task by the construction crew. As each step is completed, that is documented as a mini-milestone which represents a percentage of the total installation process. The percentage given for each subtask can vary based on the project and this progress is usually agreed on to be used as a measuring took beforehand. A good way to implement this method in Primavera P6 is using Activity Steps.

 

3. Start/Finish

This method is only focused on capturing the starting point and the finishing point of the task and nothing in between. This method is best for tasks that are short in duration. You would implement this method if the task’s work estimations are not available or if the percent complete progress data is too difficult to collect.

“Classic examples include testing services such as load test on electric panels, flushing and cleaning of piping, and similar tasks.”1

Using the Start/Finish technique, we earn a percentage of progress when the task starts and the other half is earned once the task is complete. These percentages are determined by the owner and contractor of the project.

Often, companies agree to use the standard 50/50 Rule or other rules:

50/50 Rule – once started, the task is marked as 50% complete, and the balance is earned at final completion of the work.

20/80 Rule – used to track higher value tasks that takes a longer time to reach completion.

0/100 Rule – this rule illustrates that once 100 percent of the task is completed, only then will the value be earned. An example of this is in testing or experimental tasks since you cannot get results until the task is completed.

 

4. Cost Ratio

The Cost Ratio method is usually implemented on a project that has tasks that tend occur over a long phase or the entire project. Often used for Overhead costs, this technique is measured based on the budgeted allocation of dollars vs. the labour hours of production. This method gives the contractor the ability to earn value that is equal to the overall percent of project completion.

“For example,[] if the overall progress of the project was determined to be 42 percent, then the contractor would have earned 42 percent of the overhead and fees.”1

 

5. Experience/Opinion

Unlike the methods above that rely on definitive data, this method is relies on the experience and subjectivity of the project manager. This technique is used for tasks such as dewatering or frost removal/protection. It’s not usually recommended and tends to be seen as the last resort because each individual’s experiences and opinions vary from one another and can cause conflict between owners, contractors and architect.
 

6. Weighted or Equivalent Units

This method was highlighted as the best technique in the text and is the one that requires more effort, but also extends to a wider data range. The tasks that are being calculated tend to occur over a longer duration time and includes multiple subtasks, where subtasks can have different units of measurements.

The example used to illustrate this method is building a structural steel package. In order to complete this project it requires various units, labor hours, resources and subtasks. So to calculate the subtasks, it’s weighted on the estimated level of efforts in labor hours or by monetary value that is particular to each subtask. Once the weighted value is determined, it’s converted to reflect that value in units of measure specific to the task – and for this example, the units of measure would be tons. So once each subtask has been completed, the weighted tons (units of measure) is then converted to the equivalent units of percentage complete of the overall project.

These 6 methods for measuring project progress are commonly used in Construction project management and filter into a process of determining a percentage complete for the project as a whole using Earned Value Management.

Which of these methods do you the most on your projects?

Is Retained Logic the best Scheduling Option in Primavera?

Primavera has three Scheduling Options to choose from when you are scheduling your project. Retained Logic is the default scheduling option. When you are building a Baseline, the default option works fine. But things change when you start updating your project, activities start getting delayed and do not get executed as planned.  You then have to make a decision on whether you want to continue using Retained logic or choose Progress Override or Actual Dates as your Scheduling Option. A lot has been discussed over the internet forums on which option is the best for a project and Retained Logic has won with an overwhelming majority. But I have a different opinion.

Read the blog here

From Amit Parmar em www.theprimaverablog.com

Using Physical and Duration Percent Complete Types In Primavera P6

If you are looking for a quick way to update the progress of work on your Primavera P6 schedule or you want to describe the progress of work that has a non-uniform production rate, then you should become familiar with the different Percent Complete Types offered in Oracle Primavera P6.

Here we will start with the situation where you already have a schedule and associated baseline. There is demand for accurate, weekly updates on your project and you need an efficient and accurate way of modeling activity progress. This is where the different Percent Complete Types in Primavera P6 come in rather handy.…

See the article on the Tensix Consulting blog site.

A useful exercise would be to take the example schedule used in this article and provide weekly updates to it, comparing your results to those in this article.