Is there like a master ruler? Who decided what a length a cm, mm and inch would be and why?
In: Other
Much of the world adheres to OIML recommendations for measurement.
Length measures are largely addressed by OIML-R35
https://www.oiml.org/en/files/pdf_r/r035-1-e07.pdf/@@download/file/R035-1-e07.pdf
Edit: yes, there are master standards (measures) for most types of measurements (length, mass, volume, etc.). These are used for intermediate verifications and are often referred to as transfer standards. The actual measurement realization is usually from a scientific process that is repeatable. These are considered the ‘base units’. For example, the definition for length was changed from a physical standard (prototype of the metre) to a certain number of wavelengths of a spectral line of a krypton-86 radiation, making it derivable from universal natural phenomena. Volume as mentioned previously is actually a measurement derived from length.
https://en.m.wikipedia.org/wiki/2019_redefinition_of_the_SI_base_units
So there USED to be a master ruler. And a master gram, and so on. The standard was invented by the French after the revolution to stop confusion and bad faith acting in business. I blank on why these exact lengths were picked, but they were, and master copies were made and kept under glass.
The problem with physical objects is, they decay. Atoms at a time, when kept well, but still decay. And the more industrial and scientific the metric system became, the more important it became for these standards to remain static.
One by one, mathematicians have found mathematical formulas that are tied to a basic universal fact rather than an object.
In the case of length, a meter is defined as the distance light can travel in a vacuum in 1/299792458 of a second.
I’m no expert, but I’m pretty sure the ‘master ruler’ is actually a guy named Carl Friedrich Gauss, and his mates who hung out in a German beer hall, arguing over beer about what a meter should be. Apparently, they decided on the length of a bit of metal they found lying around, and then just kinda… ran with it. No big deal, just a bunch of dudes making arbitrary decisions about the fabric of space-time. Now we’re all stuck with it!
Actually, yes!
For example, the kilogram was originally defined in 1795 during the French Revolution as the mass of one litre of water. In 1799 they decided that everyone would refer to a single platinum block as THE definitive kilogram, and copies were based on this example.
Likewise, machinists who need standardized lengths can resort to gauge blocks. It’s a little suitcase full of metal or ceramic bricks that have been cut to an absolutely ridiculous degree of precision (0.05 micrometers). They are so perfectly flat that if you press two of them together the individual atoms will start to behave as if they are one solid object and you have to exert force to break them apart.
There are still physical meters and physical gram standards. These are measured against the physical constants that define the unit of measure. Then another physical standard is measured against the first physical standard. That second physical standard may then be distributed to a calibration lab, who will then compare your instrumentation, perhaps a caliber or a load cell, against that second physical standard. Through this entire chain, data is kept about the comparisons between each standard, all the way back to the original constant. Each link in the chain introduces a small amount of measurement uncertainty that adds up.
I am reminded there’s this Adam Savage video where he is shown a [Standard Yard](https://www.youtube.com/watch?v=vKbD0V8NvNU) by a curator.
[removed]
Yes there was, the meter and other basic units had physical standards but the are subject to wear and variations no matter how small so we gradually changed to definitions based on universal constants
There used to be master rulers, and master weights and various other objects off of which basic units of measurement were derrived and other instruments were calibrated from. But that was very unreliable. Most of these were made of metal. Their size could change from the temperature or from decay as the metal slowly rusted over the years. So scientists have embarked on the task of defining all major units of measurements through universal constants. For some this was easy and has been done, but some units still remain.
I read a book all about this a few years ago. Title was something about measurement or precise measurement. Fascinating.
Latest Answers