The process that uses the MPS as demand, explodes the bill of material for specified MPS items, nets those requirements against on-hand inventory and existing open orders, and recommends placing new production and purchase orders and changes to existing orders based on parameters that consider safety stock levels, lot sizes and lead times. It is based on the idea of dependent demand (demand for an item is due to its usage in other items) and starts at the highest level in the bill of material, stopping at the first level where the quantity of inventory plus incoming receipts is adequate to meet demand and it is not necessary to send a requirement to the next lower level. While sometimes considered complex due to many levels in the bill of material or a large number of items, MRP in general is just a calculator and depends completely on the accuracy of the MPS, bills of material and order date and quantity information to be useful.