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

 

Oracle Primavera P6 Version 21 Date Picker Box Enhancement

1          Introduction

In P6 Version 20 and earlier users could not see the time when setting a date when the User Preferences were set not to show the time. Often when setting an Actual Start of Finish date, Suspend or Resume date, constraints dates etc. P6 would pick an irrelevant time such as midnight. This is because P6 does not have the feature of Default Start time or Default Finish time found in other products like Microsoft Project.

2          Issues Created by not seeing the time when setting a date

As a result:

  • Actual dates were set at midnight and one day activities had a zero actual duration,
  • Suspend dates were set at the beginning of the day and not the end and Resume dates were set and the end of the day not the start of the day and
  • Constraints were set at midnight, so there was one extra day of negative float.
  • Project Must Finish dates were set at midnight allowing one day less for the project.

3          P6 Version 21 Date Picker Enhancement

P6 Version 21 introduced a function titled 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.

This function allows the user to see the time when setting a date even when the User Preferences are not set to show the time.

4          P6 Version 20 and earlier the time is not available

The picture below shows in P6 Version 20 and earlier the time is not displayed when setting a date:

Oracle Primavera P6 PPM Professional Date Picker Version 20 and earlier

Oracle Primavera P6 PPM Professional Date Picker Version 20 and earlier

5          P6 Version 21 the time may be set from the Date Picker box.

The picture below shows in P6 Version 21 that the time is now displayed when setting a date:

Oracle Primavera P6 PPM Professional Date Picker Version 21

Oracle Primavera P6 PPM Professional Date Picker Version 21

6          Authors Comments

This is a great enhancement as P6 usually picks the wrong time when setting Actual dates, Constraints, Suspend and Resume dates when the time is not set to be displayed from the User Preferences.

But, I still recommend that users should always display the time when editing a schedule, so they are able to see if activities are not starting at the start of the day of finishing at the end of the day.

A pdf of this article may be downloaded by clicking on this link: >>>>>>>>>>>

Paul E Harris

Director Eastwood Harris Pty Ltd

10 June 2022

99 Tricks and Traps for Oracle Primavera P6 PPM Professional Updated for Version 21 - The Casual Users Survival Guide

99 Tricks and Traps for Oracle Primavera P6 PPM Professional Updated for Version 21 – The Casual Users Survival Guide

Planning and Control Using Oracle Primavera P6 Versions 8 to 21 PPM Professional

Planning and Control Using Oracle Primavera P6 Versions 8 to 21 PPM Professional

Maintain Relationships with External Projects When Importing from Primavera XML Files

Oracle Primavera P6 Version 21 introduced a new function titled Maintain Relationships with External Projects When Importing from Primavera XML Files.

When you import projects from a Primavera XML file, you can choose whether to retain relationships between activities in the project and those in external projects.

To download this paper and understand this function please 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

Oracle Primavera P6 PPM Version 21 Activity Critical Path Toolbar

Oracle Primavera P6 Version 21 introduced a new toolbar titled Activity Critical Path.

The help file does not explain how the option operates and some of the options are not very initiative. I have documented this toolbar functions in my new Version 21 book and this paper is an extract from this book. To download this paper please 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

Dissolving Activities and Retain Lag in Oracle Primavera P6 PPM

When an activity is deleted then a chain of logical activities is broken. The Edit, Dissolve command and the right-click Dissolve command will delete an activity and joins the predecessors and successors with a Finish-to-Start relationship.

P6 Version 19 introduced the ability to retain lag when dissolving activities and this paper which is a extract from my P6 book explains how the P6 Retained Lag function operates, click on this link>>>.

The aim of this paper is to explain how the new P6 Retain Lag function operates.

When Retain Lag is selected from the User Preferences, Calculations tab, the dissolved activities predecessor and successor lags will be added together to calculate the lag in the new relationship. You will see that the predecessor and successor lags are added together.

By default, Retain Lag is not switched on and has to be activated by the user from the User Preferences, Calculations tab.

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