You're quite right that currently the measure of mass is comparitive; that is, a standard Kilogram is by definition equal to the mass of a physical object (and by extension the various replicas of it that exist outside of France).
There is nothing sacred about the amount of mass that is in a kilogram; much like the second and the meter and the pound, these are all units that have evolved from organic measurements (e.g. the physical length of a foot) and been more and more precisely defined as demanded by technology.
So what does it mean if the Standard Kilogram changes over time? As you noted, not too much for the purpose of everyday life. but what does it mean for Science?
The quantity of mass in a kilogram doesn't alter symbolic or exact relationships; no Laws of physics on the books are going to be invalidated. The only place error can be introduced is in calculations that arrive at some number. In such a case, error could indeed propagate relative to all other calculations done with the original unit. The new definition of mass would need to be used to adjust all the empirical "constants" Engineers work with every day, such as density (kg/m^3).
But since the variation in the Standard Kilogram is almost immesurably small, there isn't any consequence for everyday engineering, which is pretty approximate anyways.
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Okay now that the boring stuff is out of the way, I say Fie on this fancy Imperial mode of measurements. Let's get back to some Traditional units of American measure, as proposed by Thomas Jefferson in 1789: Follow along! I make learning FUN
2 quarts make a pottle, while 4 gills make a pint. 8 gallons make a wet firkin, and two wet firkins make a rundlet or kilderkin or a dry strike.
Two wet kilderkins make a cry coomb or a wet barrel, whereas two dry coombs make a wet hogshead or a dry quarter, each of which is a quarter ton.
a wet hogshead and a third make a tierce, while two wet hogsheads are a pipe or a butt or puncheon.
And two butts make a ton.
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