Surface plate is a precision measuring tool that is used in various industries to measure the flatness of surfaces. It is a flat, rigid, and smooth surface made of high-quality material such as granite or cast iron. The surface plate is designed to provide a reference surface for measuring the flatness of various objects.

Measurement of Flatness:
The flatness of an object can be defined as the degree of uniformity of its surface, and it is measured by comparing the object's surface with the reference surface of the surface plate. A flat object will have no deviation from the reference surface, while a non-flat object will show deviations that can be measured using various instruments.

Uses of Surface Plate:
Surface plates are used in various industries, including engineering, manufacturing, and quality control. Some of the common uses of surface plates are:

1. Inspection of machined parts for flatness and parallelism
2. Calibration of measuring instruments such as height gauges and dial indicators
3. Checking the straightness of machine tool ways and guide rails
4. Checking the squareness of machine parts and assemblies
5. Testing the roundness of cylindrical parts

Conclusion:
In conclusion, surface plate is an essential tool that provides a flat and reliable reference surface for measuring the flatness of various objects. It is used in various industries to ensure that the manufactured parts meet the required specifications and standards.