Volumetric flow is related to the use of a mathematical formula requiring a constant volume between two levels in the wet well. Most of the time it is not possible to get this constant volume when the influent pipe is between the operating levels of the pumps. This situation requires the derived flow algorithm. The Mermaid software uses both the volumetric and derived flow algorithms to generate all of its analysis and reports. Mermaid can also use the volumetric formula for part of the pump cycle and the derived flow formula for other parts of the cycle.