Distribution Key - Distributing Capacity Requirements 
The chronological distribution of capacity requirements over the duration of an operation depends on the capacity category.

The personnel capacity of a set-up person is required at the beginning of an operation and the machine operator perhaps every four hours to check up on progress, but the machine capacity is required constantly during the whole operation.
The distribution of capacity requirements in capacity planning is controlled by distribution keys
You can enter and edit the following distribution keys in the
Capacity overview screen :Distribution keys are defined in Customizing for Work centers by choosing Define distribution key.
For more information about distributing capacity requirements, see the R/3 Library PP - Capacity Planning