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Kilogram Conflict Resolved At Last (nature.com)
An anonymous reader writes: As the capabilities of science and engineering expand, they rely more on the precision of measurements. It's vitally important, then, to make sure the standard units underpinning those measurements don't change. This is a problem for the kilogram. For years, it has remained the only SI unit based on a physical object — a small cylinder of platinum and iridium. Scientists have been arguing about how to replace it for decades, but now it looks like their efforts are finally reaching fruition. They finally have all the data they need to define the kilogram with mathematical constants, which solves the problem of the variability of physical objects. "One method, pioneered by an international team known as the Avogadro Project, involves counting the atoms in two silicon-28 spheres that each weigh the same as the reference kilogram. This allows them to calculate a value for Avogadro's constant, which the researchers convert into a value for Planck's constant. Another method uses a device called a watt balance to produce a value for Planck's constant by weighing a test mass calibrated according to the reference kilogram against an eletromagnetic force." Further research has narrowed down the value of Planck's constant, and experimental data from standards bodies is finally matching up. "If they are proved right, in 2018, Le Grand K will join the meter as a museum piece."
Does this mean the US can now join the rest of the metric world, or are we still in the quagmire?
It goes back further than that. The Mendenhall Order switched the US from having physical reference artifacts for the yard and pound to basing them on the metre and kilogram way back in 1893. The US has been officially metric behind the scenes for 122 years.
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The (to me dubious) advantage of dividing by low primes pales utterly when you need to quickly calculate how much water you need in your dam to last through winter, or any other quick conversion between dimensions involving volume, area or anything else which is not in discrete units - and since you don't measure oxen or days in meters or kilos I fail to even see how your examples apply.
Plus, plug SI into Metric and quickly, in your head, with only moving zeros calculate how much energy is required to heat some water, from that how long it will take given a specific wattage, or how much a given volume of water weighs (and if you can recall its density, thus how much something else weighs) and from that how much force it will exert on the surface it sits on, and how hard it will hit an object if it falls a certain distance, or pretty much any other physics calculation - with no constants involved for moving in SI (except for material conversion, such as density).
It's simply astonishing how difficult such calculations are in Imperial, and how simple they are in Metric and SI.
so base 210 (7*5*3*2) would be an even better one
This is why the mile is 32*3*5*11 feet. OK, so the 11 is actually in there for different reasons than divisibility: there was a tradition of measuring any goods with 10-20% slop built in for spoilage. For land, a furlong (220 yards) gives you a 200 yard field with room to build a fence or road, and still have room to turn the oxen for the next furrow over. (An acre, BTW, is a rectangle a furlong by a surveyor's chain - a very handy unit for land measurement at the time.)
It's not entirely a coincidence that a furlong is very close to 200 meters. That was a strong influence in making the meter somewhat larger than the yard.
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