I've learned to add an accumulator to multiple cells using the
code on http://www.mcgimpsey.com/excel/accumulator.html

Private Sub Worksheet_Change(ByVal Target As Excel.Range)
     Static dAccumulator As Double
     With Target
       If Not Intersect(.Cells, Range("C8:O9")) Is Nothing Then
           If Not IsEmpty(.Value) And IsNumeric(.Value) Then
              dAccumulator = dAccumulator + .Value
           Else
              dAccumulator = 0
           End If
           Application.EnableEvents = False
           .Value = dAccumulator
           Application.EnableEvents = True
        End If
     End With
  End Sub

I was able to get it working for the cells I needed, but I would like
accumulators running on multiple cells (all running a separate
accumulator).  What do I need to change in the code to accomplish this?

The cells I need this for are C8 through O8 & C9 through O9

As it is set up now if I enter the value "5" into cell C8 and then add
another "5" into cell C8 then the new value is "10", which is great.
But when I also try to enter the value "5" into cell C9, the new value
becomes "15" instead of "5".

Thanks!