Chief, couple options here.
Pop open the custom/historical real time report in screen painter. You can grab the calculation here.
If it is a standard report, you can view the field in the Supervisor reports manual... the templates are there.
Concerning the refresh. More then likely, the report is refreshing to the interval (15, 30, 60) whichever is established. I have seen reports capable of doing the running day total, but they have been done in designer... which I have never seen used by the reader boards.