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Retain or Override

The question is logical

FEATURED PAPER

Stephen J.C. Paterson

HuaHin, Thailand

 



Abstract

Retained logic or Progress Override, one of the most emotive subjects when it comes to discussing how to update a schedule, all driven by one issue, performance out-of-sequence work. The author reviews the three schedule calculation options offered by Oracle’s Primavera P6, ‘Actual Dates’, ‘Retained Logic’ and ‘Progress Override’ and their effect on the earned value calculations. Six scenarios have been developed and tested on an activity within two identical schedules, one with an out-of-sequence activity and one without an out-of-sequence activity. The results of the effects on the earned value cost profile for each individual scenario are presented along with summarization of the results in a clear and concise manner. Using SWOT analysis as a basis, the paper concludes with a recommendation for a ‘best tested and proven’ practice for fellow practitioners, project management, to adopt when performing schedule updates, and for software solution providers to consider for their future releases of their products.

Keywords: Cost Profiles, Earned value calculations, Actual Dates, Retained Logic, Progress Override, P6, Primavera, Schedule calculations, Scheduling, SWOT analysis

Introduction

Having been classed as being from the Jurassic period by my juniors when scheduling is discussed, remember the days prior to the software era when networks was performed using ‘Activity-on-Arrow’ (AoA) or ‘Activity-on-Node’ (AoN) techniques, while embracing the new software era it’s not without its pitfalls. It may be the case these were there in the past but because planners and schedulers provided better detailed schedules based on numerous meeting between discipline engineers and managers to get buy-in to a final product. Running through the software package developments saw the use of Artemis [1] (mainframe then PC), Primavera [2] (Dos then Windows), eventually all the way through to Oracle’s Primavera P6 [3] as we know it nowadays.

Potentially one if not the most contentious item when calculating the schedule during an update, especially when out-of-sequence activities are contained within the network, is what calculation method should be used. The Oracle P6 User Guide mentions very little about the subject, while within the industry there are differing opinions as to which method is better.

The Problem statement to be reviewed in this paper is “What is the impact of each method on the calculations of earned value?”

Specifically, this paper wants to conclude with a set of guidelines or “best tested and proven” practices as well as some recommendations for software solution providers regarding the use of Retained Logic and Progress Override.

The Methods Available

The use of retained logic or progress override methods is normally associated with the discovery of ‘out-of-sequence’ work in the network. This is not an uncommon occurrence in construction industry as these tend to crop up when an activity has been identified that can be commenced ahead of the original planned sequence in the schedule network.

For example; two activities ‘A’ & ‘B’, based on the schedules original network, activity ‘A’ (the predecessor) was required to complete before activity ‘B’ could commence. However, after some analysis it was determined by the construction team that since activity ‘A’ had progressed past a certain point, that activity ‘B’ could commence before activity ‘A’ finished, so the decision is made to commence activity ‘B’. When the P6 schedule update is performed, it recognizes that the network logic has not been honored and flags an ‘out-of-sequence’ activity as an error on the schedule log it produces. Chances are that the logic in the original schedule was defective when it was developed.

When activities are in progress, Oracle P6 provides three calculation methods when performing the schedule update process, refer to figure 1.

These choices are:

  1. Actual Dates: Forward and Backward passes are scheduled using the actual dates. Uses the network logic and same rules as retained logic.
  2. Retained Logic: Uses the network logic for the activity and it will not schedule the activity until all the predecessor(s) are completed.
  3. Progress Override: Network logic ignored allowing the activity to progress without delay.

By offering these three options, updating schedules can have differing results when using them.

As the author mentioned above the Oracle P6 v15.1user guide [4] is not very forthcoming with the calculation methods. The P6 online guide which appears when the ‘Help’ icon is pressed provides the following; “Schedule calculations provides three methods to choose. Specify the option to be used to schedule the activities in progress. Choosing Retained Logic, the remaining duration of an in-progress activity will not be scheduled until all predecessors are completed. Choosing Progress Override, ignores the network logic and the activity progresses without delay. Choosing Actual Dates, forward and backward passes use actual dates.” [5]

More…

To read entire paper, click here

 



About the Author


Stephen J.C. Paterson

HuaHin, Thailand

 


Stephen Paterson
is an Oil and Gas professional with 35+ years of experience in project controls and construction management. Born in the Highlands of Scotland, he served an apprenticeship and gained a Higher National Certificate in Civil Engineering in the UK, before embarking on the adventure of expat living, working worldwide; Middle East, North & South America, Russia, Middle East, Far East, South East Asia, China and Australia. He just completed his last assignment in February of 2017, and currently, furthering his education by way of a distance learning mentoring course, under the tutorage of Dr Paul D. Giammalvo, CDT, CCE, MScPM, MRICS, GPM-m Senior Technical Advisor, PT Mitrata Citragraha, to attain Guild of Project Controls certification.

Stephen lives in HuaHin, Thailand and can be contacted at sjptain@aol.com