part 2: p6™ calculations · p3 v p6 cpm calculations measure – one-day start 02apr14 08:00...
TRANSCRIPT
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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