Once planning is calculate, a quick reverse planning is done, from end to start (taking only calculated duration of tasks), to determine latest start and end dates.
When planned dates are equal to latest dates, activity is on the critical path.

This means that if on task included in the critical path extends, whole projects extends of same duration.

Ok,

but when there are none contiguous task in critical path, there is problem no ?
like when the planned end date of the first task is before the planned begin date of the next task, the critical path seem to not be display.

example in your projeqtor demo :
the task with wbs : 99.2.1 is the first task of an task chain. this task is none contiguous with the next task (wbs: 99.3.1) and it's not in critical path. but the task (wbs: 99.3.1) that is contiguous with the next step task, is in critical path.

It's normal ?

Regards
vlepetit

Yes, it's normal.

Concider that task 9.2.1 extends of 1 day : end date of project does not change.
So this task is not on critical path

Now, extend task 9.3.1 of 1 day : end date of project is delayd of same duration.
So this task is on critical path.

ok i understand !!

thank you !