By default, the Actual Cost column is locked down in Project Professional both at the task and assignment level. Actual Cost is calculated from Actual Work and Fixed Cost values. This way, the relationship with Work done and cost accrued remain consistent.
Ground realities are many times more complex and actual costs involve Journaling, currency conversions and other adjustments. This is typically handled in ERP systems and all a PM wants to do is to manually enter the actual cost value in Project so that she can track the remaining cost.
To enter the actual costs manually, you need to change the following setting in Project Professional.
1- Go to File- > Options –> Schedule.
2- Scroll to the bottom of the page till you reach the last section “Calculation options for this project:”
3- Uncheck the box “Actual costs are always calculated by Project”
4- This will change the setting for Current Project only. If you want this setting to be applied to all Projects, then change the drop down value in front of “Calculation options for this Project” to “All Projects”
Some points to consider in this approach are:
1- Actual cost will only be editable from Project Professional. It will still not be editable from PWA
2- Project Manager will need to manage actual costs for each cost based assignment. Automatic work based calculation will be turned off for entire project.
– See more at: http://epmadvice.blogspot.com.au/2014/09/how-to-manually-edit-actual-cost-in.html#sthash.MyKKo1rN.dpuf