Manometers can be specifically used to measure what kind of pressure?

Manometers are versatile instruments designed to measure the pressure of fluids. The correct choice indicating that manometers can specifically be used to measure both positive and negative pressure highlights their practical applications in various scenarios.

Manometers consist of a U-shaped tube filled with a liquid, typically water or mercury. When measuring positive pressure, the pressure applied to one side of the U-tube raises the liquid level on the other side, providing a direct correlation to the pressure exerted. Conversely, when measuring negative pressure (or vacuum pressure), the pressure inside the system being tested is lower than the atmospheric pressure, resulting in a change in liquid levels that can also be quantified. This dual capability makes manometers particularly valuable in both laboratory and industrial applications.

In contrast, other choices represent more specific limitations: absolute pressure is measured with instruments designed solely for that purpose and typically requires a different setup compared to manometers. Variable atmospheric pressure deals with fluctuations in atmospheric conditions rather than a particular measurement device. Static pressure, while relevant in certain contexts like fluid dynamics, does not encompass the full range of pressures that a manometer can measure, especially in relation to the negative pressures involved. This makes the chosen answer the most fitting representation of a manometer's functionality.