unit of measure problem in COR6N

hi,

I have one scenario where base unit of measure of material is KG whereas in BOM it is maintained as gm.I have 1kg of stock but in COR6N when i put 500 gm systme is not allowing it to do so.

So my question is whether the system will automatically convert or consider alternative unit of measure or else we must define alternative unit of measure in additional data in material master?