What are the top mechanical measuring instruments?

A measuring instrument is a tool to gauge any physical quantity. They are used in every field, like physical sciences, quality assurance, engineering, and in the manufacturing of buildings. They all have some SI units and standards by which the whole world gauges or measures the specific quantity they are made. The measuring instruments have special test methods by which they are standardized. They all have the least count. They all may have some kind of uncertainty fixed after taking the measurement. All objects, from rulers to large instruments like electron microscopes, are measuring instruments.