Introduction:
Mechanical gauges are devices used for measuring pressure or force by converting them into mechanical motion. They rely on mechanical components to provide accurate measurements. Among the given options, the mechanical gauge is the one that fits this description.

Explanation:
The correct answer is option 'C', which is the Bourdon tube. Let's understand why the Bourdon tube is a mechanical gauge.

Bourdon Tube:
The Bourdon tube is a mechanical pressure gauge that was invented by Eugene Bourdon in the 19th century. It consists of a hollow, curved tube that is typically made of metal, such as brass or stainless steel. The tube is closed at one end and connected to the pressure source at the other end.

Working Principle:
When pressure is applied to the open end of the Bourdon tube, it tends to straighten out due to the internal pressure. This causes the tube to deform, and the amount of deformation is proportional to the pressure being measured. The deformation of the tube is converted into a rotational movement through a series of linkages and gears.

Indicator Mechanism:
The rotational movement is then transferred to a pointer or a dial mechanism, which provides a visual indication of the pressure reading. The pointer moves over a calibrated scale, allowing the user to accurately read the pressure value.

Advantages:
- The Bourdon tube is simple in design and reliable.
- It can measure both low and high pressures accurately.
- It can withstand harsh environments, making it suitable for various industrial applications.

Limitations:
- The Bourdon tube is susceptible to mechanical wear and fatigue over time.
- It may exhibit hysteresis, which means that the indicated pressure may differ slightly when the pressure is increasing or decreasing.

Conclusion:
In conclusion, the Bourdon tube is a mechanical gauge used for measuring pressure. It relies on the deformation of a curved tube to convert pressure into mechanical motion, which is then indicated on a scale. The Bourdon tube is widely used due to its simplicity, reliability, and ability to measure a wide range of pressures.