A drip gauge may be used to measure?

A drip gauge is specifically designed to measure the amount of fuel in a tank, typically by tracking the flow or accumulation of fuel as it is dispensed or used. This tool provides a visual representation or direct measurement that allows operators to determine fuel levels accurately.

The other options pertain to different characteristics of fuel. For instance, measuring temperature requires a thermometer rather than a drip gauge, while pressure in the tank is assessed with a pressure gauge. Viscosity, which refers to the thickness or flow characteristics of the fuel, also requires specialized equipment, such as a viscometer. Thus, the application of a drip gauge is limited to the measurement of fuel quantity, making it the correct choice in this context.