I worked a lot with torque wrenches in the Army, and always wondered how the “first” torque wrench was calibrated without another one to verify that it was accurate? Was there another tool to verify the calibration was correct and if so how did that one get calibrated. In my head it keeps asking “well how did the next one get calibrated?” Every time I think about the first precision tools of any type, not just for torque.
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Depends on what it measures, but at the end of the chain we have unit definitions.
We determine the length of a meter based on time and the speed of light. The length of a second by the oscillation of a specific atom. Force is based on mass (from the kilogram) and velocity.
We create flatness using the grinding of three plates together.
Geometric shapes are formed by geometric definitions, like flat plates through grinding, while units are “formed” from principles of physics.
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