What type of reading sight glass uses a vertical pipe with a magnetic float that rides on the surface of the fuel?

The question describes a sight glass that employs a magnetic float within a vertical pipe to display the level of fuel. This setup allows for the measurement to occur without direct contact between the liquid and the gauge, which can be particularly important in applications where the fuel might be hazardous or vapor-sensitive.

In this case, the correct answer is the type of sight glass that utilizes the principle of indirect measurement by reading the position of the float through other means, such as a scale or indicator outside the pipe. This design maintains safety and operational integrity, ensuring that the reading is reliable even if the surface of the fuel is unstable or agitated.

The term "indirect sight glass" reflects this method of measurement because it does not require a clear view of the liquid itself, relying instead on the positioning of the float to convey information about the level. The magnetic aspect adds another layer of functionality by allowing the reading to be accurate and easily interpreted, minimizing the risk of errors or malfunctions associated with direct visibility or contact.

Other sight glass types, such as standard, direct, and magnetic sight glasses, would not accurately represent the specific characteristics described in the question, as they either show the liquid directly or do not incorporate a floating mechanism in the configuration specified.