WIP Calculation - Line ID for Settled Costs in transaction OKGA

Hello,

In transaction OKGA we have a line ID STL (Settled Costs) assigned to category A (Settled Costs). What does this mean? Is it included in WIP or not? If yes what is the difference with the other ligns of material costs ? Also please tell me if any Cost element is assigned to LIne ID STL, is it possible to change the Line ID to either material or labour or overheads,

Thanks,

Lavanya