Well the answer is yes you could. you would need to create some code on one of the event triggers like on insert or on current etc. You'd need to experiment to find the one that works for you. It's good to see the picture but to write code for you we would need to know exactly how your DB was structured. Is this form based on a query or direct from tables?
The way I would do this is to declare a variable and then assign the current value held in your field Dwg No something like Dwg = Me![Dwg No].Value
Then write an open record set method to get the information from your entries for this order.
tmp = "SELECT * FROM tblOrder WHERE (((tblOrder.Dwg)=" & Dwg & "))"
Set ctrl = conn.OpenRecordset(tmp, dbOpenSnapshot)
Bqty = ctrl.[Total Bal]
Me![Bal Qty] = Bqty
You’ll have to play with this idea to get it right for your situation but hopefully this may give you an idea of how to proceed with it
I am by no means an expert on this and some of the other guys on here may well have a better solution for you.