The last thing I'm trying to work out on database is the running balance.  I have played around with a lot of different ways of doing it , but seem to have a similar outcome. I put code back to this:

=IIf(IsNull([TransactionID]),"",Nz(DSum("TAmount","CheckRegQ","TransDate <= #" & [TransDate] & "# AND TransactionID <= " & [TransactionID]),""))
Work great unless you need to add an older record and don't run query by date ascending.

if you do use date ascending, it puts in date in right order, then properly adds or subtracts the amount.  After which it adds or subtracts the next record value to the prior value so the new transaction doesn't get calculated into running balance.