To determine the correct distance below the tank top for an overfill-prevention device, which chart should be referenced?

The correct answer is the placement chart because it specifically provides the necessary information regarding the appropriate distances for the installation of overfill-prevention devices in relation to the tank top. This chart is essential for ensuring that the device is positioned correctly to function effectively, which is a pivotal aspect of UST compliance and safety measures.

An overfill-prevention device's primary role is to prevent the tank from being filled beyond its capacity, thereby avoiding spills and potential environmental hazards. The placement chart typically outlines standardized measurements that must be adhered to for successful installation, accounting for factors such as tank design, size, and the type of overfill prevention system used.

The other charts listed do not focus on the specific requirements for installing overfill-prevention devices accurately. A measuring chart may provide general dimensions, a units chart could show conversion factors, and a gauging chart might depict measurement techniques for assessing liquid levels but would not address the precise spatial requirements for safety features like overfill prevention. Therefore, the placement chart is the authoritative source for determining the correct distance below the tank top.