Part 2: P6™ Calculations · P3 v P6 CPM Calculations measure – One-day start 02APR14 08:00...

2017 Construction CPM Conference

Part 2: P6™ Part 2: P6™ Part 2: P6™ Part 2: P6™ CalculationsCalculationsCalculationsCalculations

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by Ron Winter, FAACE, PSP

Schedule Analyzer Software

Ron Winter, FAACE, PSP

• Bachelor of Science in Engineering

• Construction Scheduler

• US Air Force Navigator

• Construction Scheduler

• Master of Science in Systems Management• Master of Science in Systems Management

• Programmer, Project Manager, Customer Support,

and Industrial Trainer

• Construction Scheduler

• Developer of

Schedule Analyzer Software

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• Part 1: P6 Durations and Dates

• Part 2: P6 Calculations– CPM Calculations

– Longest Path Calculations

– Multiple Float Path Calculations

Today We Will Cover

– Multiple Float Path Calculations

– Schedule Calculation Options

– Putting This All Together

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CPMCPMCPMCPMCalculationsCalculationsCalculationsCalculations

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P3 v P6 CPM Calculations

• P3 subtracts one

– Early Start + Duration – 1 = Early Finish

– 02APR14 08:00 + 1 hour - 1 = 02APR14 08:00

– Next activity Early Start = Early Finish + 1

• P6 does not subtract one but ‘overlaps’

– Early Start + Duration = Early Finish

– 02APR14 08:00 + 1 hour = 02APR14 09:00

– Next activity Early Start = Early Finish

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• If P3 Uses a Whole Day for smallest time unit:– One-day activity start 02APR14 & end on 02APR14

– Next activity would start 03APR14

• If P6 Used a Whole Day for smallest time unit:– One-day activity start 02APR14 & end on 03APR14

– Next activity would start 03APR14

• Hard to see because P6 uses minute as unit of

P3 v P6 CPM Calculations

• Hard to see because P6 uses minute as unit of measure– One-day start 02APR14 08:00 & end on 02APR14

16:00

– There is no 16:00 hour in our example calendar

– 02APR14 16:00 = 03APR14 08:00

• Therefore, time must always be shown using P6

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How P6 Calculates the CPM

• Example diagramed calculation

This is the CPM

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• Resultant re-calculation

This is the CPM

Diagram!

This is the Start &

Finish diagram!

Summary

• CPM calculations begin with the Data Date

• Every activity is calculated using

– Remaining Duration

– Existing logic

– Activities with actuals are still calculated

• Start and Finish columns show

– Early dates if not started

– Actual dates if started

• Barchart displays Start and Finish dates

• Logic is drawn between displayed bars

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CPMCPMCPMCPMCalculationCalculationCalculationCalculationOptionsOptionsOptionsOptions

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Schedule Options

To bediscussed:

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Multiple Float Paths

• Calculate multiple float paths using

– Total Float – Relationship Float

– Free Float – Longest Path

• Display multiple float paths ending with

– ‘Dangerous’ to leave blank

– Designate Substantial Completion activity

– Can use to investigate milestone completion

• Specify the number of paths to calculate

– Blank to calculate all paths

• Group activities in the Activity Table by Float

Path and sort by Float Path Order11

General Schedule Options

• Ignore relationships to/from other projects– Backups affected by setting (External Constraints)

• Use Expected Finish Dates– Option to define in schedule but not use

• Automatically level resources• Automatically level resources– Setting not exported with backups

– Optional report not automatically shown

• When scheduling progressed activities use– Retained Logic

– Progress Override

– Actual Dates12

Out-of-Sequence Progress Scheduling Options

• Retained Logic

• Progress Override

• Actual Dates

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P6 Actual Dates

• If successor (Activity 2) is incomplete

– Calculation acts like Retained Logic

• If successor is complete• If successor is complete

– Calculation acts like Progress Override

– Can create negative Total Float without constraints

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Why Use Actual Dates?

• Actual Dates with actuals in the future

• Retained Logic with actuals in the future

• Progress Override with actuals in the future

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RD=0

Calculate Start-to-Start Lag

• from Actual Start– Once started, continue

• from Early Start– Count earned lag

– Begin remaining lag

from Early Start 16

General Schedule Options

• Calculate float based on the finish date of

– Each project

– Opened Projects

• Used when multiple schedules are open

• Float based on latest finish• Float based on latest finish

– Each schedule open

– Latest schedule

• New option gives single critical path

– Longest Path still only by project

• Setting not exported in backups

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• Calendar for scheduling relationship lag

– Successor activity calendar – default pre-P6v4

– Predecessor activity calendar – new default

– 24-hour calendar

– Project Default calendar – like MS Project

• Used even for relationships with 0 lag

General Schedule Options

• Used even for relationships with 0 lag

• Finish-to-Finish always uses successor’s

calendar

– Causes discontinuous longest paths

• Always uses predecessor’s calendar for

hour/day duration conversions18

Admin TabAdmin TabAdmin TabAdmin TabCalculationsCalculationsCalculationsCalculations

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Set Baseline Source

• Make Baseline Bars show actual, not Planned Dates.

• The Earned Value tab should be set to either:either:

– At Completion values with current dates

– Budget Values with current dates

• (some versions use ‘Planned Values with current

dates’)

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Set Baseline SourceAdmen Menu /

Admin

Preferences /

Earned Value Tab

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Suggested setting

Set Baseline Source

• A Baseline is set using menu Project / Assign Baseline

– Not <Current Project> for Baseline schedule

name

• Set the Primary User Baseline name

– (Not assigned using a Layout created by

import)

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ProjectProjectProjectProjectCalculationsCalculationsCalculationsCalculations

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Unlink Remaining Duration

• Project window / Calculations tab setting / Activities

– “Link Budget and At Completion for not

started activities”

• How RD works for unstarted activities

– Checked

• Remaining Duration always equals Original

Duration

– Un-Checked

• Remaining Duration can be set different from

Original Duration 24

• Project window / Calculations tab

• Uncheck

Unlink Remaining Duration

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Longest PathLongest PathLongest PathLongest PathCalculationsCalculationsCalculationsCalculations

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Longest Path Calculations

• Longest continuous string of activities

– Determines shortest possible time to complete project

• Calculate the forward (early) CPM dates

• Find activity with latest Early Finish

• Trace a path ‘backwards’ of controlling • Trace a path ‘backwards’ of controlling

relationships

– P3 designated driving during forward pass calculation

– P6 uses activity’s Free Float

• Ignores Total Float changes due to calendars

– More accurate than Total Float < 1

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Longest Path Latest Early Finish

Sample CPM network

Longest Path Calculations

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Lowest Total Float

Note: Controlling = Predecessor activity has Zero Free Float

• Does not ignore forward-pass early date constraints

– Start On

– Start On or After

– Finish On

– Finish On or After

• Constraints can make longest path discontinuous

Longest Path Calculations

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• Constraints can make longest path discontinuous

Multiple Multiple Multiple Multiple Float PathFloat PathFloat PathFloat PathCalculationsCalculationsCalculationsCalculations

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Multiple Float Paths

• Identifies secondary critical paths

• Based upon calculating relationship float

– Calculate relationship early/late start/finish dates

– Calculates relationship Total Float and Free Float

– Dates viewable on Relationship Tab

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Relationship Float

• Relationship dates computed on start-up & re-scheduling

• Early and Late dates allow for relationship float

• Relationship float may not be same as activity floatactivity float

• Exact measurement of controlling relationship

• Basis of Longest Path Software™– Schedule Analyzer Software (released December 2003)

• Basis of P6 Multiple Float Paths™– “‘Enhanced’ PDM – Concepts and Benefits”, Scott Herold,

Black & Veach (AACE Annual Convention 2004)

– Introduced in P6 in Version 5 in 2005

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Relationship Float Example

Finish-to-start relationship with 0 lag

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Relationship Lags Visualized

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Relationships Computed

Q: Is Activity FF = Relationship Total Float?

Ans: No, lowest Relationship FF

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Types of Multiple Float Paths

• Total Float– Find latest, lowest relationship Total Float

– Follow predecessor’s lowest relationship Total Float

– Tag activity with Float Path Number

– Stop when activity does not have a predecessor

– Go back and start again with next lowest relationship

Total Float

• Free Float– (Same instructions using relationship Free Float)

– Lowest Free Float equals ‘controlling relationship’

– Float Path 1 the same as Longest Path

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Sample MFP Calculations

‘Standard’ CPM calculations showing activity Total and Free Float

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Relationship Total Float and Free Float added

Sample MFP Calculations

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Free Float Float-Path 1 Latest Early Finish Activity

Multiple Float Path 1 identified

Sample MFP Calculations

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Total Float Float-Path 1

Same example entered into P6

MFP Using Total Float

40Relationship Float for Last Activity Predecessors

Total Float/Free Float Comparisons

Multiple Float Paths – Total Float setting

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Multiple Float Paths – Free Float setting

MFP Using Total Float

Grouped by Float Path and sorted on Float Path Order

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Grouped by Float Path and sorted on Float Path Order

MFP Using Free Float

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Advanced Schedule Options

• Calculate MF Paths using

– Total Float – Relationship Float

– Free Float – Longest Path

• Display MF Paths ending with– ‘Dangerous’ to leave blank

– Designate Substantial Completion activity

– Can use to investigate milestone completion

• Specify the number of paths to calculate

– Blank to calculate all paths

• Group activities in the Activity Table by Float

Path and sort by Float Path Order44

Putting It Putting It Putting It Putting It AltogetherAltogetherAltogetherAltogether

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Putting This All Together

• P6 calculates the CPM like MS Project except

– Always begins from the Data Date

– Considers every activity using remaining duration and

logic

• Time should be shown when viewing dates

• CPM scheduling methods produce different results• CPM scheduling methods produce different results

– Retained Logic is the best method for estimating overall

schedule completion

– Progress Override allows for ‘automatic’ activity

sequence rescheduling

– Actual Dates best if actual dates in the future allowed

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• Multi-schedule programs can calculate a single

critical path using Total Float

• Relationship calendars settings can cause

discontinuous longest paths

• Also check the Admin Tab and Project Window

Putting This All Together

• Longest Path is best option for showing

remaining work

• Lowest Total Float setting is best for showing

milestone impacts

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• Multiple Critical Paths shows near-critical paths

– Uses concept of relationship float to analyze schedule

– Two major settings can produce wildly different

results

– Best to designate the path-ending activity

Putting This All Together

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Questions?Questions?Questions?Questions?

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