Table OEAUDD: diff between [UNITCOST] and [EXTCOSTH] ?

SOLVED

Hello, 

Looking at the Posting Journal table OEAUDD

Question: What is the difference between [UNITCOST] (item unit cost I'm assuming) and [EXTCOSTH] ? Initially, I thought EXTCOSTH was just unit cost multiplied by the quantity (and it is in some cases). But in other cases my unit cost will be ZERO and I'll still have an amount for  [EXTCOSTH]

Thank you,
Michelle