Which of the following is a type of fuel quantity gauge?

A sight glass is indeed a type of fuel quantity gauge commonly used in various aircraft to visually indicate the amount of fuel present in the tank. It consists of a transparent or semi-transparent tube or chamber mounted to the fuel tank, allowing the operator to see the fuel level directly. This type of gauge is simple and can be quite reliable in providing an immediate visual reference for fuel quantity.

In contrast, a digital display represents a modern method of offering real-time fuel quantity readings but does not fall under the traditional category of directly measuring fuel levels as seen through a sight glass. While it may be accurate and useful, it operates on different technology and principles.

A barometer measures atmospheric pressure and is not related to fuel quantity. Similarly, a temperature sensor measures temperature, which, while critical for various functions in aircraft systems, does not provide any information regarding the fuel level. The specificity of the sight glass to fuel quantity distinguishes it as the correct answer.