In Primavera we can define Critial activities by 2 option:
There are many reasons why we should choose Longest Path instead of Total Float. One of the reason is that when our project has multiple calendar.
We have 4 activities which have same calendar : Standard 5 day workweek. We use Total Float to calculate Critical path. The result is this:
When I change A1020 activity’s calendar to 1 Day Workweek. We use Total Float to calculate Critical path. The result is this:
You can see it’s wrong critical path.
Now when you choose Longest path option. It will become like this:
Now the critical path is better
So when you have multiple calendar project, consider to use Longest path option.