Yes, once they can perfectly count the # of atoms of silicon in the sphere, they can then know how many atoms of carbon would be in the same sphere, and/or helium, etc etc, this allows them to divide out the physical part of the equation and leave it as a constant. Therefore it cannot change with time.
FUN FACT: that ball weighs exactly 1 kilogram, and that is the base measurement for a kilogram, anything that is weighed using kilograms is being compared to that orb.
Actually a black hole is the roundest object we know of, the intense gravity pulls it in to a perfect sphere to the subatomic level.
BUT, it is the roundest man made object, so at least there's that.