Flow meters are placed on the circulation system of the pool to determine the flow rates. This tool is required at pools in many states. This is for 4″ pipe. REFUND POLICY is as follows. For CPO Services, a refund will be given prior to 14 days of the class less a $35 cancellation fee and a 5 percent credit card charge. No refund will be given in the two week period before the start of the class. For products, refunds will be given on unopened returned merchandise within 30 days of purchase minus a 15 percent restocking. Shipping fees are not refundable.