in help.sap there is an one liner which is very generic "
"help.sap says
Run safety stock planning.
Based on the settings in the location product master, the system calculates the safety stock quantities for the selected product and locations.""
also there are phrases like time dependent and time independent .
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but i have created one key figure in planning area from standards for safety stock ..after running the 500 should settle down in that safety stock filed