What is the primary instrument used to measure test pressure?

The primary instrument used to measure test pressure is a manometer. A manometer is specifically designed for measuring pressure differences between two points and is commonly used in various applications, including plumbing, gas installations, and laboratory settings. It typically consists of a U-shaped tube filled with liquid, where the height of the liquid column indicates the pressure difference.

In contrast, a thermometer measures temperature, an abacus is a counting tool used for arithmetic calculations, and a barometer measures atmospheric pressure. While a barometer does relate to pressure, it is not typically used for measuring test pressures in closed systems or specific applications where a manometer is more appropriate. Thus, the manometer's unique design and function make it the ideal choice for accurately measuring test pressure.