Reference Indicator 
You can set a reference indicator for each default value in a work center and thus specify that the default value is referenced in the task list. This means that:
The default value can only be changed in the work center and not in the task list.
A change in the work center is automatically transferred to the task list, when the task list is called up.
If you remove the reference indicator in the work center, you can then change default values in the task list.
Caution
If you change data in the work center, only the data with a reference indicator is changed in the task list. The data in the operation is brought up-to-date the next time the task list is called up.
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A reference indicator is set internally by the system for keys of performance efficiency rate .