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Please help me explain in Actiivity ID A1020 (highlighted) why Total Floats become bigger as my "Act % Comp" is bigger and lesser when % is lesser? I used Retained Logic but even if I will use "Progress Override", i get the same Total Float. They are of the same Data Date. I am so confused. I need your help.
Warren Sika
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Deleted by Rafael Davila as to avoid annoying requests to revive this discussion as it is older tha 3 years.
So old no longer Photobucket pictures are available.
Take a look at the following schedule. I split Activity 3 into 2 activities, Activity 3a with start links equal to Activity 3 start links, a FS(0) between splits, Activity 3b with finish links equal to Activity 3 finish links, duration of Activity 3a + 3b = duration of Activity 3.
It could have been that instead of splitting into two activities splitting into three could make it also, but you got to control the split into chunks that are reasonable, chunks that make sense. Because splitting is not as efficient as if continuous performance it might be that some extra duration must be added.
Now you can see only second split is critical, now it is easier to follow logic, even when activity 3b can potentially still show reverse logic. I would never delete the FF link if this is the logic of my schedule, I would only consider splitting the activity on my own terms, knowing how duration and resources are distributed.
FF links are very powerful, very useful and convenient but you shall know the implications. If still needed do not delete them just use them wisely.
Dear Sir Rafael Davila,
Thank you very much for that wonderful job of letting me understand.
I am using P6 and unfortunately those "darkened links" you're saying is not probably available in P6 but I can tell now why those floats behaved that way.
One more thing, right now I found out one of my work program schedule is having a reverse logic, how can I correct it as the work progress? Shall I delete links FF? What can you suggest?
By the way, I am just new to P6. This "interruptible duration option" is not yet known to me. I will try to explore more. Thanks PP!
Warren
Dear Sir Rafael Davila,
Thank you very much for that wonderful job of letting me understand.
I am using P6 and unfortunately those "darkened links" you're saying is not probably available in P6 but I can tell now why those floats behaved that way.
One more thing, right now I found out one of my work program schedule is having a reverse logic, how can I correct it as the work progress? Shall I delete links FF? What can you suggest?
Warren
Add two SS Links as follows.
Change duration of Activity 2 to 10 days and re-schedule, you shall get something as per following figure. You will notice some links have darkened, because they are connecting critical activities the ones that are darker are driving and critical. You got several critical paths as links is what connect paths, without links you have no paths.
Now increase duration of activity 3 to 15 days and re-schedule. You will notice darker links changed, your critical path changed. You have FF predecessor of Activity 2 as driving. So at this moment activity 2 is active in reverse logic, if you increase its duration a few days its start will move to the left but its finish will not move.
Whenever you have FF or SF links these activities can be on active reverse logic or might be inactive/dormant with respect to their potential for reverse logic. If you filter links that are FF or SF type, that are driving, then you will get a list of active reverse logic links, some might be critical and some might not. The following figure shows the full table, if hundreds of activities I would execute the filter, I left the table unfiltered intentionally for you to compare the links properties.
There is a lag value that can tell you how much you can increase an activity with an active reverse logic predecessor until its start no longer moves to the left, this value is not available in any software I know, Spider Project I believe is about to include it along with another that is also related to it.
You avoid the possibility of reverse logic if there are no FF/SF links. If your software have the option for Interruptible duration as P3 does it will mask the reverse logic, it will work as if you split the activity. This might be an alternate logic you might want, the problem is that it does not tells you how the activity was split.
Let me know if your software has the interruptible duration option and with your help as I do not have P6 we can explore the two options.
Dear Sir Rafael Davila,
It really did. Wow! I don't know that. How we avoid and determine this reverse logic? Can you continue? Thanks.
Warren
Please model the following within your software.
Then increase duration of Activity 2 to 10 days. What happened to project duration?
If by increasing Activity 2 duration you decreased project duration you got reverse logic active on the critical path.
Can you tell me which is the critical path? There is a catch on my question. Most people will say Activity 1, Activity 2 and Activity 3, but this is not a path, just the activities, 50% of it, the critical links do matter. Latter will add some additional links and see what happens to the project duration and critical path.
Dear Sir Rafael Davila,
Thanks for the effort you did. I am enlightened a little. Can you expound more bye doing that sample?
God Bless You!
Warren
Warren,
How reverse logic will impact your schedule will depend on the available float to the left of some activities, one of many float values not shown or perhaps not even defined by most software.
At times reverse logic will impact a few activities but not the critical path; at times it will impact the critical path.
I received the file and found that Activity A1030 is driven by the FF link coming from Activity A1020. If you increase remaining duration of Activity A1020 the link will delay Activity A1030. But here is the catch if you increase remaining duration of Activity A1030 for up to X days it will be able to start earlier before its finish is delayed.
These X days are a float value to the start of an activity that will tell how much the activity duration can be increased to the left before the reverse logic is no longer driving. This float value is not shown in any of the software I know and seems like it will be available soon for Spider Project. This X days value might change if you switch the retained logic and progress override options.
Because Retained Logic add some invisible constraints to the schedule in order to try to solve the out-of-sequence the remaining portion of some activities might be delayed as well as the project finish. This can create a shift in the critical path complicating the understanding of what is happening. I suggest fix logic as to avoid out-of-sequence. The following screen is of your file without displaying activity names, it show how values of float changes if using Retained Logic on the Current Schedule versus if using Progress Override on the Baseline Schedule. Still other software have more options other than Retained Logic ande Progress Override such as P6 and Spider, I suspect Asta PP also have more than two options, none a sure fix.
As I said before, you have out-of-sequence and reverse logic on your schedule. None are bad, any type of link can cause the out-of-sequence, but you need links. The only way to avoid 100% out of sequence events is to have no links at all, no schedule at all. Reverse logic can be avoided if you avoid SF and FF links, but these links are needed at times, the issue is how to tame them. For me disclosing the float to the left would be enough.
If you still feel like you do not get it, if you want we can try modeling a very simple schedule of about 4 activities and make changes to it as to explore what I mean by reverse logic. Let me know.
Best Regards,
Rafael
Dear Sir Rafael Davila,
Can I have your email address? Can I send my program instead so that you will full understanding with my problem. my email address just in case you need it. warrensick@yahoo.com
Actually, my only concern is why floats are not behaving the way it is expected to. Why my TF become bigger when it should have been become lesser if bigger accomplishment is entered.
Thanks.
It looks like:
If your software have the option for Interruptible duration as P3 does I would try it, just remember in such case you will be moving from contiguous to interruptible schedule computations. If this solves/mask the issue I would consider splitting the activity on my own terms rather than staying with interruptible mode but that would be a separate issue. In addition, if this solves the issue I would recommend fixing the out-of-sequence logic as it can always be a distraction and will always use retained logic option and will use progress override for comparison only.
I said "mask" because the only way to prevent reverse logic effect is by avoiding SF and FF links, it might be that for some increase in activity remaining duration it will have no noticeable effect on other activities. Keep in mind that if percentage complete is linked to remaining duration then by changing %complete you are changing remaining duration.
I would consider temporarily eliminating the constraints for an easier understanding on what is driving the schedule.
Best Regards,
Rafael
Dear
Mr. Rafael - "Note started but not finished Activity A1020 finish does not change with a change in % complete." The Finish date is driven by the Predecessor A1010 (Pile Caps) with FF25. I understand that, that is why the Finish Date is 13Mar13 + 25days = 07Apr13.
Mr. Gary,
1. There is no constraint created here.
2. You are right, it is itself an out of sequence activity. But how to correct it, can you tell me? Do I have to remove the Predecessor SS31 in the update Programme? I tried it but it gave same outcome.
3. They have similar changes, calendar used. No resource and cost loaded.
4. I use Duration for % complete type and Fixed Duration & units for Duration Type.
5.
Thanks all.
It might be convenient to display remaining duration along with the bars and links. If your software is capable of displaying markers for date constraints it would also help, otherwise display date constraint columns.
Note started but not finished Activity A1020 finish does not change with a change in % complete.
In some occasions reverse logic if impacting critical path might reduce project/phase finish and this is a rare but possible cause. Activities with a FF predecessor and a SS successor are prime suspects of reverse logic.
With simple filters you shall be able to identify the activities with FF predecessors and SS successors.
http://www.youtube.com/watch?v=pihBXqRWoik
It might be reverse logic is via SF successor, just adjust your filter to identify the activities with FF predecessors and SS/SF successors.
In any case look for unstarted successors.
Good luck.
Warren,
The fact that it is ngative float suggest it is being driven either by a constraint, or out of sequence logic
1) Check the activity and any succesors for constraints
2) check the predeccesors for out of sequence working, and correct any errornous relationships
3) Check which (if any) activities downstream of this activity have similar changes in float when this activity % compelte is adjusted, what relationship types are being used, and what calendars (activity and resource) are assigned
4) Check what % complete type you are using (duration, units or physical)
5) Let us know what you find, and we should be able to help you further
Cheers,
G
Email: PPadmin@planningplanet.com
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