Feels like a chicken and egg senario. Let’s say I get my torque wrench from work sent off to be calibrated, and that’s calibrated with something itself needs to be calibrated, and so on and so fourth. How’s that figured out?
In: 430
It’s important to remember that all measurements have an associated uncertainty. This includes the fundamental definitions for the seven base units such as length, time, mass, temperature, etc.
These base units are only redefined when we find a better method which results in a reduced uncertainty or easier implementation, etc. We just went through this with mass, the last base unit defined by a physical artifact. For a lot of reasons we don’t want base units defined by physical artifacts which can be lost or damaged. Work has been ongoing to redefine the kilogram for many years and just recently a method with better uncertainty and that can be realized by various labs around the world.
At all but the national research labs (NIST, NRC, etc) physical standards are still used – in fact even NIST and NRC use physical standards for most of their day to day work. Weights and measures inspectors for example use various grades or levels of stainless steel and cast iron standards depending upon the level of traceability required. High precision standards will be used to test precious metal scales and lower precision, but still calibrated and traceable, cast iron standards are used to test and calibrate larger freight and vehicle scales.
Canada’s K50/74 prototype kilograms are physical artifacts that are still the primary reference standards for the country. All other mass standards are compared to these standard. It is only when the primary standards need to be tested (they are never adjusted) that the kibble balance (new definition) would be used. Previous to this, the international prototypes were physically carried to Sevres, France for comparison with the international prototypes kilogram (colloquially le grand K)
https://en.m.wikipedia.org/wiki/International_Prototype_of_the_Kilogram
Feels like a chicken and egg senario. Let’s say I get my torque wrench from work sent off to be calibrated, and that’s calibrated with something itself needs to be calibrated, and so on and so fourth. How’s that figured out?
In: 430
It’s important to remember that all measurements have an associated uncertainty. This includes the fundamental definitions for the seven base units such as length, time, mass, temperature, etc.
These base units are only redefined when we find a better method which results in a reduced uncertainty or easier implementation, etc. We just went through this with mass, the last base unit defined by a physical artifact. For a lot of reasons we don’t want base units defined by physical artifacts which can be lost or damaged. Work has been ongoing to redefine the kilogram for many years and just recently a method with better uncertainty and that can be realized by various labs around the world.
At all but the national research labs (NIST, NRC, etc) physical standards are still used – in fact even NIST and NRC use physical standards for most of their day to day work. Weights and measures inspectors for example use various grades or levels of stainless steel and cast iron standards depending upon the level of traceability required. High precision standards will be used to test precious metal scales and lower precision, but still calibrated and traceable, cast iron standards are used to test and calibrate larger freight and vehicle scales.
Canada’s K50/74 prototype kilograms are physical artifacts that are still the primary reference standards for the country. All other mass standards are compared to these standard. It is only when the primary standards need to be tested (they are never adjusted) that the kibble balance (new definition) would be used. Previous to this, the international prototypes were physically carried to Sevres, France for comparison with the international prototypes kilogram (colloquially le grand K)
https://en.m.wikipedia.org/wiki/International_Prototype_of_the_Kilogram
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