Scheduling terms
A dependency says which activity has to move before another one can. Every first Gantt chart is built from four of them, finish-to-start, start-to-start, finish-to-finish and start-to-finish, each with an optional lag. Here is what each one means with a jobsite example, and how to set them on an activity in Fidrel.
30 days free · No long-term contract.
A first schedule often chains every activity finish-to-start, because that is the one link people already know. The plan then runs longer than the job will, since work that could overlap, like ductwork rough-in starting while framing is still going, is forced to wait its turn.
When concrete has to cure or an inspector has to come, the wait gets added to the activity’s duration. The bar looks longer, the work looks longer, and nobody can tell later that those days were a wait and not labor.
Dates typed by hand look like a plan until one activity slips. With no links behind them the successors do not move, and the superintendent finds out two weeks later at the lookahead meeting.
Finish-to-start (FS) is the starting value: the successor starts after the predecessor finishes, as when drywall hanging starts once the framing inspection is done. In Fidrel an FS link with no lag starts the successor on the next working day, because bars include both their first and their last day. Start-to-start (SS) lets two activities run side by side: ductwork rough-in can start a few days after framing starts. Finish-to-finish (FF) ties the endings together: the punch walk cannot finish before commissioning finishes. Start-to-finish (SF) is rare; temporary power cannot be shut off until the permanent service has started. A finish-to-start link from a milestone releases the successor on the milestone’s own day, since a milestone has no duration.
Scheduling
Lag is entered in working days of the project’s calendar. A lag of 3 on a start-to-start link starts the successor three working days after the predecessor starts, and weekends and the non-working dates in the working calendar are skipped on the way. A curing time that runs through a weekend therefore has to be entered as the number of working days it spans. Keep waits like this in the lag and not in the activity’s duration, so the bar shows the labor and the lag shows the wait.
Step 1
Open the activity that has to wait and find its Dependencies fields. Click Dependencies to add a row, then pick the Predecessor from the list of the other activities in the plan.
Step 2
Set Type to FS, SS, FF or SF and enter the Lag (working days) beside it. Leave the lag at 0 when the successor can follow straight away, or enter the number of working days it has to wait.
Step 3
Save the activity and look at the chart. Successors move forward automatically when the link requires it, and the plan refuses a cycle or a link to a group, so a bad link shows up at once.
A group, meaning a parent activity with subactivities, cannot be a predecessor or a successor, so link its subactivities instead. A cycle, where A waits for B and B waits for A, is refused with a message to check dates, hierarchy, calendar and dependencies. Moving a predecessor later pushes its successors forward automatically. Once the links are in, the critical path marks the activities that have no float, which is the quickest way to see which of your links actually decide the finish date.
A plan saved from Microsoft Project as XML brings its tasks with each link’s type and lag, rounded to whole working days. Fidrel keeps its own working calendar and does not read the one in the file, so set the calendar after an import and look at the dates once more.
Lag is counted in working days only, not in calendar days or as a percentage of the predecessor. When a predecessor is moved earlier, its successors keep their existing dates. Two activities can be linked only once in the same direction, and a group of activities cannot be linked.
Your trial applies to your first own project and starts when that project is created. No card required. Afterwards, choose card or invoice to continue.
The project system of the future connects people, documents and decisions. Discover the thinking behind Fidrel.
Read more
On site, answers need to be close at hand. Fidrel displays DWG drawings in your mobile browser, within the project’s document structure.
Read more
When everyone can see the next step, moving the project forward becomes easier. Fidrel brings activities, dates and reported progress together in a shared Gantt view.
Read moreScheduling terms
Anything else on your mind? We are happy to help.
Talk to usIn a finish-to-start link the successor waits until the predecessor is done. In a start-to-start link the successor only waits for the predecessor to begin, so the two can overlap, optionally after a lag.
No. Lag in Fidrel is entered in working days of the project’s working calendar, so weekends and the non-working dates you have added are skipped when the successor’s date is worked out.
Use start-to-start with a lag when the second trade can begin once the first has made some headway, and finish-to-finish when the second trade cannot finish before the first one does.
It refuses a cycle, a second link between the same two activities in the same direction, and a link to or from a group. Link the subactivities instead, and check that no chain leads back to its own start.
Yes. A plan saved as XML brings each link with its type and lag, rounded to whole working days. The working calendar is not read from the file, so set Fidrel’s calendar after the import.
Nothing moves by itself. Successors move forward automatically when a link requires it, but when the predecessor moves earlier they keep their existing dates until you move them.
