Definition of metric units
Metric units aren't defined by Le Grand Kilo anymore as it's not a suitable way of ensuring that you get a perfectly reliable reference.
It's currently defined by taking the fixed numerical value of the Planck constant h to be 6.62607015×10−34 when expressed in the unit J⋅s, which is equal to kg⋅m2⋅s−1, where the metre and the second are defined in terms of c and ΔνCs.
That may sound complicated, but it gives you a unit that's usable for extremely accurate scientific use that's not just based on some lump of metal.
The meter is defined as the length of the path travelled by light in vacuum during a time interval of
1/299 792 458 of a second.
The major advantage of the metric system for end users is that the units are interrelated and easy to calculate with. You're not left dealing with base 12 or base 16 and fractions and all sorts of crazy historical units. Familiarity doesn't mean they're easy.
I mean we used a currency, the Pound, that until the early 1970s had 240 pence in each pound and 12 shillings and prices were written like £1 2s 3 1/2d = One pound, two shillings and 3 and a half pence. People thought that was fine and you had holdouts claiming decimal money was far too complicated. They also used tons of jargon like Half Crowns, Thruppeny Bits and then also used Guineas (one pound and one shilling!)
Also the A standard of paper used in Europe makes sooooooo much sense! I have no idea how Americans work with that arbitrary system of paper sizes when dealing with things like say a photocopier to enlarge something.
Take A0 (large format drafting paper). Fold it in half and you have A1
Fold A1 in half and you have A2
Fold A3 in half and you have A4 (the stuff we mostly put in printers)
Fold A4 in half and you have A5
And so on.
Metric units aren't defined by Le Grand Kilo anymore as it's not a suitable way of ensuring that you get a perfectly reliable reference.
It's currently defined by taking the fixed numerical value of the Planck constant h to be 6.62607015×10−34 when expressed in the unit J⋅s, which is equal to kg⋅m2⋅s−1, where the metre and the second are defined in terms of c and ΔνCs.
That may sound complicated, but it gives you a unit that's usable for extremely accurate scientific use that's not just based on some lump of metal.
The meter is defined as the length of the path travelled by light in vacuum during a time interval of
1/299 792 458 of a second.
The major advantage of the metric system for end users is that the units are interrelated and easy to calculate with. You're not left dealing with base 12 or base 16 and fractions and all sorts of crazy historical units. Familiarity doesn't mean they're easy.
I mean we used a currency, the Pound, that until the early 1970s had 240 pence in each pound and 12 shillings and prices were written like £1 2s 3 1/2d = One pound, two shillings and 3 and a half pence. People thought that was fine and you had holdouts claiming decimal money was far too complicated. They also used tons of jargon like Half Crowns, Thruppeny Bits and then also used Guineas (one pound and one shilling!)
Also the A standard of paper used in Europe makes sooooooo much sense! I have no idea how Americans work with that arbitrary system of paper sizes when dealing with things like say a photocopier to enlarge something.
Take A0 (large format drafting paper). Fold it in half and you have A1
Fold A1 in half and you have A2
Fold A3 in half and you have A4 (the stuff we mostly put in printers)
Fold A4 in half and you have A5
And so on.