Application; Excel 97. I am trying to create a spreadsheet to calculate total gallons of throughput in a system. I have actual flow rate (gpm) streaming into a cell in real-time. I am multiplying that cell by another that has elapsed runtime (min) being inputted. The product of this formula is total gallons. (gpm x min = gallons) The problem occurs when the flow rate is reduced to a lesser value. Excel automatically lowers the product to a new lower value of gallons. In reality, the gallons have already flowed and are not reduced. How do I get Excel to calculate the cumulative total of gallons that have flowed over time independent of the present flow rate?