NEW_COST and PRIOR_COST columns in MTL_MATERIAL_TRANSACTIONS table

Hi,

I would like to know how are PRIOR_COST and NEW_COST columns getting populated in MTL_MATERIAL_TRANSACTIONS table.

We have a custom form which is based on Miscellaneous transactions form, INVTTMTX.fmb (Inventory responsibility) where we are populating Unit Cost field. The original form, INVTTMTX.fmb does not populate Unit Cost field. The only way I see MTL_MATERIAL_TRANSACTIONS table getting populated is through our custom form. We are populating Actual_Cost and Transaction_Cost columns in MTL_MATERIAL_TRANSACTIONS  but I am not sure how Prior_Cost and New_Cost columns are getting populated. Any help is much appreciated.