Logic links: one side's delay disappeared, the other kept all of it
A first delay pushes completion by 5 days. Then a second delay of 20 days lands on the same activity, and whoever holds the sequence changes two downstream links from finish to start into start to start. Predict how far completion moves the second time, then watch it move 20 days, 10, or none at all as the count of changed links runs from 0 to 2. The 20 days are still sitting in the activity, and a reading that looks only at the finish date cannot see them.
Your prediction before the experiment
What stays fixed
- Precondition
- The same activity scope and information in every reading
- Activities
- Excavate, Support, Pour
- Base durations
- 10 days each
- First delay
- 5 days on Excavate
- Second delay
- 20 more days on Excavate
- Reference
- Both original links after the first delay
The relationship reading
Changed downstream links
One changes Support to Pour first. Two then changes Excavate to Support. The order never changes.
This recalculates the typed three activity network after the exact link changes shown here. It assigns no responsibility, judges no relationship, decides no entitlement, and takes no view on which links in real work are physical.
Here is the maths
The formula, in words
The reference completion uses the first delay and both original finish to start links. The current completion uses both delays and the selected changes. The latest finish among all three current activities is retained, then the reference completion is subtracted.
where is incremental movement, the latest current finish, and the reference completion after the first delay.
A worked example
- The three base durations are 10 days. After the first 5 day delay, the reference completion is 35.
- The second delay makes the first activity last 35 days. With both original links, completion is 55 and movement is 20.
- Change Support to Pour and completion is 45, so movement is 10. Change Excavate to Support as well and the latest finish is 35, so movement is 0.
What this does not model
The calculation accepts exactly three named activities and exactly two downstream relationship positions. It does not decide who controls a relationship, whether a relationship is reasonable, or whether the resulting overlap can occur in real work.
Source basis
Published scheduling mathematics and delay analysis guidance supply structural context for chosen sequence logic, date effective correction, and visible relationship change records. The lesson reproduces no source wording and teaches no generic path switch or revision trace.
This lesson does not assign a relationship to a party or classify one as justified, compensable, compliant, or physically necessary. Fields asking for those conclusions are refused rather than ignored.
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