Once there were seven artifacts in the weights
and measures family.
Along with the kilogram, there was the candela,
which measured luminous intensity, the kelvin
(temperature), the metre (length), the ampere
(electric current), the mole (substance) and
the second (time).
Science has since quantified all other base
units in terms of mathematical constants
leaving the kilogram as the only material artifact
remaining in the current system of units.
Strangely it affects three of the base units
of measure the mole, ampere and candela
which says NIST, are all linked to the weight
of those 40 blocks of platinum-iridium.