FlowVis Flow Meter 1-1/2" for Swimming Pools. Perfect for pools with Variable Speed Pumps. The FlowVis is a combination of a pool flow meter and check valve that provides you with the flow rate of your system. Which is extremely when calculating the ideal amount of flow to turn over the pool water. It features a sleek design. The FlowVis Flow Meter reads the flow in GPM's and includes scales for key velocity points. By using a swimming pool flow meter to know your GPM, you can dial in your swimming pool pump and maximize energy savings by slowing the variable speed pool pump to its lowest required speed for filter circulation.