What the use of Item Opening Balance in inventory & how to d

Question

What the use of Item Opening Balance in inventory & how to do

 

I have created a apps called inventory.

 

The transaction are

 

PO

Good Receive Note[GRN]

Good Issue Note[GIN] 

 

When transaction of  GRN created then the stock will added(+) into Mst_Stock Table

 

When transaction of GIN created then the stock will Minus(-) from Mst_Stock Table.

 

Then how and where to do the opening balance of each item

 

My Mst_Stock Table is

 

StockNo

ItemNo

StockQty

 

Thanks

Basit.