Which of the following measurements would not be best performed with a differential manometer?

A differential manometer is specifically designed to measure pressure differences between two points, making it useful for various applications involving pressure measurements.

The measurement of the vacuum of a venturi generator is a situation where the differential manometer is not the best instrument to use. While it can measure pressure differences, the vacuum conditions might require more specific instruments tailored to high accuracy in low-pressure environments, such as an absolute pressure gauge or a vacuum gauge. In contrast, other situations, such as measuring the static pressure of an air plenum or the pressure drop across a filter, directly lend themselves to the capabilities of a differential manometer, as they typically involve comparing two pressure points effectively.

For fluid power system pressure, while it can also be measured with a differential manometer, general hydraulic pressure measurements can often be more effectively managed with standard pressure gauges. Thus, in cases involving vacuum measurements like that of a venturi generator, different methods are favored over the differential manometer.