>The yard or the metre shall be the unit of measurement of

>>9108409
Rulers and scales

>>9108409
Avoirdupois measurements are shit and can only be derived precisely from metric (Si) units, unless you want to steal a bar of silver from France.
A gram is defined as the weight of one cubic centimeter of water, of course then you have to define the length of a centimeter, so you use the speed of light for a fraction of a second, but then how do you define a second?
The answer is to shut the fuck up and just finish your homework.

>>9108437
We are talking about times when there were no electronic weight scales.

>>9108461
Oh how were they measured, meticulously using repeated torsion balances for mass with mirrors on n shit. Length was done by calibrating from defined standards - possibly again using light as it travels in straight lines. But that's only down to 10ths of a mm so not that accurate

>>9108456
Length is defined by the speed of light, time is defined by the radiation of the ground state of Caesium 133, electric current is defined by the force between two ideal wires, temperature is defined by the triple point of water, the mole is defined by a the number of atoms in a kilogram of carbon-12, and the candela is defined by the luminous intensity of a specific frequency of light.
The only measurement that is yet to be given a definition free of a physical object is the kilogram, and scientists are looking to rectify this.

>>9108531
Do you realistically think a reform is possible?

>>9108409
Imperial units are defined by metric units nowadays

>>9108580
They did it for every other unit. All that changes is the definition; there were plans to make the kilogram be based off of the Planck constant a couple of years ago, but the data was not robust enough for the change to be made. The next meeting will occur in 2018.
In the life of the layman, nothing will be different if the change is made, since the resulting error is much smaller than the tolerances of any industrial process.

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68KB, 750x625px

>>9108531
Christ, physicists truly are retarded: none of those are definitions. They are measurement standards.
One is compelled to ask again: how do you define the metre or the second?

>>9108580
>literally normalfag brainlet YouTube viewer tier
https://www.youtube.com/watch?v=Oo0jm1PPRuo
he's made a million videos about the kilogram and its redefinition

>>9108596
>redefinition
restandardisation*

>>9108595
>>9108600
You may be confusing your terminology. The unit has a definition, and the method within the definition is known as the standard. For instance, the metre is defined as:
>... the length of the path travelled by light in vacuum during a time interval of 1 ⁄ 299792458 of a second.
In this case, the standard is the fraction of the distance travelled by light in a second.
As such, the true terminology when changing the description of a unit is redefinition, because it is the change from one standard to another.