Believe the planners shall avoid using the negative lag with FS relationships. Try positive lag with SS relatioship and close the open end with reasonable positive lag FF relationship.
As a layman, owner might feel that negative lag with FS relationship can mislead the schedule or the logic of work is not retained.
Bernard, thanks for the link to the interesting discussion at PMI COS.
I think the simplest explanation (other than software functionality) for avoiding negative lag (in any type of relationship!) is that it triggers an activity start or finish on the basis of an event that has not yet occurred. That necessarily increases risk, as the triggering event may NEVER occur! That said, I have occasionally used negative lag in situations where I felt that any other modeling method represnted an even greater distortion.
As to the discussion at PMI COS, Id just mention that one of the drawbacks of using any complex dependencies (SS, FF, SF) and/or lags is that it can make the task of manually computing critical path DRAG very difficult.
Negative lag is allowed only in certain cases.if the completion of an activity is delayed by its predecessor then you can never start the activity and hence the activity goes out of sequence. Eg:Commisioning of Substation if Panels are not installed.
One more reason to not allow the contractors to use negative lag in general that the most of the time it is used for manupulation to meet the target dates initially.
Maybe we should ask why we us Lag. We use lag positive or negative if the schedule is not broken down to enough detail. Unfortuanatly when we start projects engineering has not been done we do high lvl schedule (Lvl 1/2/3)in this case lag is used.
Once detail is developed these lags normally drop away.
To have a rule no -lag is allowed I think is unrealistic. (You can apply a rule in lvl 3/4 schedule no - lag is allowed only if this is part of your definition for a lvl 3/4) In planning we use all kinds of Methods and if we stop using negative lags we stop using a planning method so then we can just as well stop planning.
If you ever wondered the best reason for negative lag is due to the rate of progress. This minimise cost P & G. for following contracts.
I just looked into the Primavera Knowledgebase and found that there is a small bug with Monte Carlo and negative lags on finish-to-finish relationships. The successor activity finishes on the correct day, only one minute earlier than it should. I can’t recall seeing a finish-to-finish relationship with a negative lag on any schedule that I have ever dealt with. Otherwise, I did not find any other issue mentioned. By the way, is that product even for sale anymore?
I did not see any such problems with the other Monte Carlo software sold by other vendors. Is this the only issue with negative lags?
What is the relationship? FS, SS or FF, the use of negative lag is only acceptable in the case of FS. Some programs such as pertmaster, does not even accept 0 lag in the instance of SS or FF, when risk analysis is carried out. What is the clients reasons, for objecting to negative lag? Is it due to a problem during risk assesment or just a personal preference?
I am not sure why the owner does not allow it but I THINK it has to do with the detail. If you have a high lvl schedule you apply - Lag. If you get to a detailed schedule - lag dropp away becuase of the detail. So all i think the owner is telling you if you need negative lag the activity is not broke down to enough detail.
Spider Project is most functional and powerful professional project management software.
The first SP version was launched in 1993 and since then it has been constantly improved. Today is used in 34 countries though most Spider Project customers are in Russia. Spider Project offers numerous unique functional features and is the only PM software that optimizes resource, cost, and material constrained schedules and budgets for projects and portfolios.
The unique features of Spider Project include Quantity Based Scheduling, Conditional Scheduling, Skill Scheduling, Optimal Resource, Cost and Material Leveling, Resource Critical Path Calculation, Cash and Material Flows Calculation and Management, Trend Analysis, Advanced Risk Simulation and Analysis, Calculation of Success Probability Trends, Calculation and Management of required Project Time and Cost Buffers, Application of Corporate Norms, Management of many Parallel Budgets, Multiple WBS and many others.
Spider Project was and is used for management of many large scale programs in Russia, including $51bln construction program for 2014 Winter Olympic Games preparation.
The application areas where Spider Project is successfully used include Aerospace, Banking, Construction, Defense, Energy, Engineering, Infrastructure, Manufacturing, Metallurgy, Mining, Oil & Gas, Railways, Retail, Shipbuilding, Software Development, Telecommunications, Utilities, etc.
P6-Auditor - Display information from Primavera P6 audit tables in a user-friendly format
Unifier-Archiver - Extract and archive important documents and attachments from Primavera Unifier
Unifier-Loader - Load data into and out of Unifier via Excel
PCM-Loader - Import data into Primavera Contract Management with flexible and secure, template-driven Excel spreadsheets
PCM-Archiver - Extract and archive important documents and attachments from Primavera Contract Management
PCM-Unifier Migrator - Automatically transfer live and historical data from Primavera Contract Management to Primavera Unifier with ease
Create Radically Better Construction Schedules with ALICE Technologies
Use the power of AI to create construction schedules that reduce risk while cutting costs and build time. With ALICE, develop the ideal schedule during preconstruction -- or recover projects that are off schedule and over budget.
Believe the planners shall avoid using the negative lag with FS relationships. Try positive lag with SS relatioship and close the open end with reasonable positive lag FF relationship.
As a layman, owner might feel that negative lag with FS relationship can mislead the schedule or the logic of work is not retained.
Bernard, thanks for the link to the interesting discussion at PMI COS.
I think the simplest explanation (other than software functionality) for avoiding negative lag (in any type of relationship!) is that it triggers an activity start or finish on the basis of an event that has not yet occurred. That necessarily increases risk, as the triggering event may NEVER occur! That said, I have occasionally used negative lag in situations where I felt that any other modeling method represnted an even greater distortion.
As to the discussion at PMI COS, Id just mention that one of the drawbacks of using any complex dependencies (SS, FF, SF) and/or lags is that it can make the task of manually computing critical path DRAG very difficult.
Negative lag is allowed only in certain cases.if the completion of an activity is delayed by its predecessor then you can never start the activity and hence the activity goes out of sequence. Eg:Commisioning of Substation if Panels are not installed.
One more reason to not allow the contractors to use negative lag in general that the most of the time it is used for manupulation to meet the target dates initially.
Hi Bill
Strange Rule of Thumb.
Maybe we should ask why we us Lag. We use lag positive or negative if the schedule is not broken down to enough detail. Unfortuanatly when we start projects engineering has not been done we do high lvl schedule (Lvl 1/2/3)in this case lag is used.
Once detail is developed these lags normally drop away.
To have a rule no -lag is allowed I think is unrealistic. (You can apply a rule in lvl 3/4 schedule no - lag is allowed only if this is part of your definition for a lvl 3/4) In planning we use all kinds of Methods and if we stop using negative lags we stop using a planning method so then we can just as well stop planning.
If you ever wondered the best reason for negative lag is due to the rate of progress. This minimise cost P & G. for following contracts.
Cheers
Heres a similar topic being discussed at the PMI COS:
Negative Lags of Finish to Start Relationships
Bernard Ertl
eTaskMaker Project Planning Software
I just looked into the Primavera Knowledgebase and found that there is a small bug with Monte Carlo and negative lags on finish-to-finish relationships. The successor activity finishes on the correct day, only one minute earlier than it should. I can’t recall seeing a finish-to-finish relationship with a negative lag on any schedule that I have ever dealt with. Otherwise, I did not find any other issue mentioned. By the way, is that product even for sale anymore?
I did not see any such problems with the other Monte Carlo software sold by other vendors. Is this the only issue with negative lags?
Bill,
You say the risk analysis cannot be done on a negative lag? This is very interesting. Can you expound more on this? Thanks in advance.
Hi Guys,
What is the relationship? FS, SS or FF, the use of negative lag is only acceptable in the case of FS. Some programs such as pertmaster, does not even accept 0 lag in the instance of SS or FF, when risk analysis is carried out. What is the clients reasons, for objecting to negative lag? Is it due to a problem during risk assesment or just a personal preference?
Regards
Philip
I am not sure why the owner does not allow it but I THINK it has to do with the detail. If you have a high lvl schedule you apply - Lag. If you get to a detailed schedule - lag dropp away becuase of the detail. So all i think the owner is telling you if you need negative lag the activity is not broke down to enough detail.
Hope this helps