Accumulating totals from a set date

Is there a way to have a tag that would add daily totals of another tag from a set date such as DLYTONS?  For instance starting today, the tag would only be today’s DLYTONS at the BOD.  Tomorrow it will be that DLYTONS BOD plus today’s.  Three days from now, the tag would add it's existing value plus that day's DLYTONS BOD total…  This would continue until we decide to reset the start date or reset the value to zero (whichever would work).

Our Results Supervisor does this in Excel right now used for a ratio in his reports.  We are retiring his thousands of Excel sheets by moving the equations into PI but this one has stumped me.

I hope I made sense.

Thanks