Manometers are devices used to measure the pressure of liquids and gases. They work based on the principles of hydrostatics, which states that the pressure at any point in a fluid at rest is the same in all directions. Manometers consist of a U-shaped tube filled with a liquid, usually mercury or water, and the pressure difference between the two ends of the tube is measured by the difference in the levels of the liquid in the two arms.

The liquid used in manometers should have high surface tension. Surface tension is the property of liquids that allows them to resist an external force, such as gravity. The surface tension of a liquid is determined by the cohesive forces between the molecules of the liquid.

When a liquid is used in a manometer, it should form a meniscus at the point where it meets the glass tube. The meniscus is the curved surface of the liquid that forms due to the difference in the adhesive forces between the liquid and the glass tube. The surface tension of the liquid affects the shape of the meniscus, which in turn affects the accuracy of the pressure measurement.

If the liquid used in a manometer has low surface tension, it will not form a well-defined meniscus, and the measurement of the pressure difference will be inaccurate. On the other hand, if the liquid has high surface tension, it will form a well-defined meniscus, and the measurement of the pressure difference will be more accurate.

Therefore, the liquid used in manometers should have high surface tension to ensure accurate pressure measurements. Some common liquids used in manometers with high surface tension include mercury, water, and oil.