Causes of Negative Float in Oracle Primavera P6

1          Introduction

I recently had a discussion with a student who was trying to track down the reason for Negative Float on an activity and I decided to write this article as a check list for people who want to track down the cause of Negative Float in their program.

There are a number of reasons why a P6 program will display Negative Float, some are well known and expected, some less well known and some not expected.

The text below is a summary of the causes but my full article may be found here:

https://eastwoodharris.com/DL/TP/2200826_P6_Negative_Float_Causes.pdf 

2          Aim

The aim of the article is to list the reasons why a P6 program will display Negative Float under the following headings:

  • Well Known and Expected,
  • Less Well Known and
  • Unexpected

3          Negative Float Definition

There are not very many definitions of Negative Float in documents that have a list of scheduling definitions and AACE Recommended Practice 10S-90 Cost Engineering Terminology defines it in the as:

  • The amount of time by which the early date of and activity exceeds its late date. It is how far it is behind an activity is behind its planned early start/finish date.
  • Time by which the duration of an activity has to be reduced in order to permit a limiting imposed date to be achieved. (June 2007)

Scheduling software calculates Negative Float when the Lates Dates are earlier that the Early Dates and is calculated by the subtraction of the Late Finish minus the Early Finish calculated over the calendar assigned to the Activity.

The issue of why a schedule has Negative Float is as a result of the algorithms that the software used to calculate the Late Finish.

You may wish to buy one of my P6 book by clicking on this link below to learn more about how P6 works:

 

4          Well Known and Expected

4.1            Activity Constraints

Setting a Finish Constraint such as a Finish On, Finish On or Before or Mandatory Finish before the calculated activity Finish Date will generate Negative Float.

4.2            Project “Must Finish By” Date

Setting a Project Must Finish By date will generate Negative Float:

5          Less Well Known

5.1            Setting a Constraint without Displaying the Time

When a user is not displaying the time and when they set the Finish On or Before constraint the software set the time to be midnight at the start of the day and thus the Finish of the activity is calculated at the evening before resulting in negative float.

5.2            Project “Must Finish By” Date Without Displaying the Time

Setting a Project Must Finish by Date without showing the time will also set the Project Must Finish Time at midnight. This again will create Negative Float when the Project Must Finish By date is set at the same date as the calculated finish date but at Midnight at the start of the day.

5.3            External Relationships

When a project has link to a project with successors activities that have a constraint the negative float will be reflected in the predecessor project’s activities:

When the project is opened on its own the Negative Float is still calculated:

But if you check the Tools, Schedule, Options, Ignore relationships to and from other projects, then relationships from other unopened projects are ignored:

5.4            External Constraints

When a project is exported and imported into another database the missing external relationships are replaced with External Early Start and External Late Finish constraints which will create negative float.

The External Constraints may be deleted but if you check the Tools, Schedule, Options, Ignore relationships to and from other projects, then the External Constraints are also ignored which is not clear from the option title:

6          Unexpected Reasons for Negative Float

6.1            Setting Multiple Baselines

When you open multiple projects and set the baselines for all the projects then restoring these baseline projects will create ghost relationships and the restored projects and current projects may not calculate correctly and may create Negative Float in any of the projects.

6.2            Inprogress LOE Activity

When an LOE activity has progress and the Schedule Options are the Default there is no Negative Float on LOE activities. But if the Schedule, Options for Compute Total Float as bare are changed to Strat Float = Late Start – Early Start then Negative Float is calculated on the LOE activity although the Late Start and Start are the same, but the Early Start is actually the Remaining Early Start and thus the Negative Float.

6.3            Finish Milestones and Lags

There has been a longstanding issue with Finish Milestones with a predecessor that has a Lag and another calendar which often calculate Negative Float.

The issue can be resolved by changing the Finish Milestone to a Start Milestone.

6.4            Schedule Options and Circular Relationships

When the Scheduling, Option, When scheduling progressed activities use is set to Actual Dates then often Negative Float is generated and also Circular Relationships may not be identified. Please read my article Understanding the P6 Scheduling Options “When scheduling activities use, Retained Logic, Progress Override or Actual Dates” by clicking on this link:

https://eastwoodharris.com/DL/TP/190416_Understanding_P6_Schedule_Options_When_scheduling_activities_use.pdf

 

Understanding Oracle Primavera P6 Duration Type

The P6 Duration Type works in conjunction with options set in the User Preferences, Calculations, Resource Assignments tab and becomes effective after a resource has been assigned to an activity.

The aim of this paper is to explain how the P6 Duration Type and the options set in the User Preferences, Calculations, Resource Assignments tab affect the resource assignment process and task resource calculations.

These options are useful to understand so when you change the duration of an activity you know if the crew size will remain the same if the work assigned to an activity will remain the same, click on this link to read the paper>>>.

Accelerate your understanding of scheduling software to advance your scheduling career and be able to prepare better schedules with Eastwood Harris books, online videos available through Udemy (search for Paul E Harris once on the site) and training material on:

  • Microsoft Project,
  • Oracle Primavera P6 and
  • Elecosoft (Asta) Powerproject

Details at  https://www.eh.com.au

Paul E Harris

Director Eastwood Harris Pty Ltd

What’s New in Oracle Primavera P6 Version 21 PPM Professional

Oracle released Primavera P6 Version 21 PPM for download from their eDelivery web site in late 2021.

Oracle has published a tool that you may use to see the enhancement that have been introduced into P6 by comparing two different versions. This is the link to the “Oracle Primavera P6 Cumulative Feature Overview”

I have written a document that expands on the documents published by Oracle and outlines the changes a PPM user will see in the software and add some comments on the usability of the features, click on this link>>>.

The aim of this paper is to explain the main functional changes that users will see in the Oracle Primavera P6 PPM V21.12 added since the release of P6 PPM V20.12.

In this paper I cover the following topics:
– Assignment Cost are Exported.
– Users may See and Set Activity Start and Finish Times in the Date Picker box when the User Preferences are set only to show the date.
– Financial Period Calendar Selection when Importing an XML file.
– Maintain Relationships with External Projects When Importing from Primavera XML Files.
– IPMDAR Format Supported for EEPM Databases only.
– Resource and Role Cost Spreads Consider Rate Changes Over Time.
– Activity Critical Path Visibility.

Accelerate your understanding of scheduling software to advance your scheduling career and be able to prepare better schedules with Eastwood Harris books, online videos available through Udemy and training material on:

Details at  https://www.eh.com.au

Paul E Harris

Director Eastwood Harris Pty Ltd

ORACLE PRIMAVERA P6 RESOURCE LEVELING FUNCTIONS

Many contractors like to level a resourced project schedule for a number of resaons, but usually to reduce resource demand to the available resources or due to site limitations such as accommodation availability.

ORACLE PRIMAVERA P6 RESOURCE LEVELING

ORACLE PRIMAVERA P6 RESOURCE LEVELING

P6 has some Resource Leveling functions and this paper which is a extract from my P6 book explains how the P6 levelling functiuons operate, click on this link>>>.

Accelerate your understanding of scheduling software to advance your scheduling career and be able to prepare better schedules with Eastwood Harris books, online videos available through Udemy and training material on:

Details at  https://www.eh.com.au

Paul E Harris

Director Eastwood Harris Pty Ltd

IMPORTED P6 PROJECTS CALCULATING INCORRECT COSTS

I was recently contacted by a client who was finding imported projects were not calculating the project costs correctly and had different values to the original project in the database that it was exported from. This article explains why imported projects may have different costs to the original project click on this link>>>.

Accelerate your understanding of scheduling software to advance your scheduling career and be able to prepare better schedules with Eastwood Harris books, online videos available through Udemy and training material on:

Details at  https://www.eh.com.au

Paul E Harris

Director Eastwood Harris Pty Ltd