When a Customer, Supplier, Nominal or Charitable fund activity is displayed have a running Balance1 of the account as an extra column after the Debits and Credits (like the Pick accounting systems had, and bank statements have).
It should total based on what is displayed (so that if filter is in place, eg only O/S [X], it sums those values) in the order they are displayed.
1a running Balance is the total of the items displayed above the line plus the value on the current line. A suffix of Dr or Cr can be added, or use of a standard, such as Credits are negative numbers, can be used.