If you update daily cost "afterwards"
=> Real cost is automatically updated to new daily cost.
=> left cost is taken into account with new daily cost.
=> assigned cost is preserved at cost know when assignment has been defined.

It behavior is not this one please, give more information (print screen for instance)

Thanks for Answer.

This is indeed not the behaviour faced. My version is v6.1.2.

As an example, see enclosed picture. The project started with resource daily costs set to 198€/day.
RealWork is 3 for an activitty started on 06/10/2016.
Then I updated daily cost to 220€ from 01/06/2016.
The Real Cost for activity is not updated and cost for the assignation is not correct. (stil

l set to 198 €).

As I previously explain, assign cost is preseved with cost defined when assignment was created.
This is normal and won't be changed (except as of ticket #2684, if cost was zero).

For real work, unfortunately your print screen dos not show costs on activity...

I did the following test :
Create new project P.
Create new resource R, with cost at 200€/day.
Allocate resource R to project P
add new activity A on project P.
Assign 3 days of work for resource R on activity A
Enter 1 real work day on march 1st, enter 1 real work day on april 1st, recalculate planning on may 1st.
This give expected result :

Then I change cost for resource R to 250€/day on march 15th.
Result is exactly as expected :
assigned = 600€ (**200)
real = 450€ (1*200+1+250)
left = 250 (1*250)

Thanks a lot .... My fault, the problem was i didn't launch a project recalculation from a date prior to the dailyCost change.
When doing this, things looks now good.
Sorry for that.