Introduction:
The device popularly used for measuring the difference of low pressure is the Inverted U-tube Differential Manometer. This device is widely used in various industries and applications where precise measurement of low pressure differences is required.

Explanation:
The Inverted U-tube Differential Manometer operates based on the principle of hydrostatic pressure. It consists of a U-shaped glass tube filled with a liquid, typically mercury or water, which is used as the manometric fluid. The U-tube is bent at the top, forming an inverted U shape.

Working:
When the pressure difference between the two points being measured is applied to the manometer, the liquid in the U-tube will move, creating a difference in liquid levels on either side of the vertical leg.

Measurement:
The pressure difference is determined by measuring the difference in liquid levels on the two sides of the U-tube. This can be done by using a scale or a graduated ruler placed alongside the U-tube. The difference in liquid levels directly corresponds to the pressure difference being measured.

Advantages:
1. High Accuracy: The Inverted U-tube Differential Manometer offers high accuracy in measuring low pressure differences, making it suitable for precise applications.
2. Wide Range of Applications: This device can be used in various industries such as HVAC, chemical engineering, pharmaceuticals, and more, where the measurement of low pressure differences is crucial.
3. Simple Design: The design of the Inverted U-tube Differential Manometer is relatively simple, making it easy to operate and maintain.
4. Cost-Effective: Compared to other pressure measuring devices, the Inverted U-tube Differential Manometer is cost-effective, making it a preferred choice in many industries.

Conclusion:
In conclusion, the Inverted U-tube Differential Manometer is the popular device used for measuring the difference of low pressure due to its high accuracy, wide range of applications, simple design, and cost-effectiveness. It is widely used in various industries where precise measurement of low pressure differences is required.