BSV's in Legal entity vs Ledger.

Hi,

The documentation says that if there is a legal entity(LE) defined in your ledger, then you must enter the BSV's(balancing segment values) first in Legal entity before you can define BSV's (not necessarily the same legal entity BSV's)  for the Ledger.

For ex, if you have a LE in your Ledger, only after you have assigned a BSV,say, '020' for legal entity, then only you can assign a value of ,say, '030' for the ledger. I know that usually for ledger, the BSV are used for adjustment transactions. 

The question is why is this functional restriction,that you have to define a BSV for LE before Ledger ?