Base SI Units
Le Systéme Internationale (SI) units are standard in science
SI system adopted in 1954.
1 second = time for 9 192 631 770 oscillations of Cs-133 excitation band radiation
1 meter = distance light travels in 1/299 792 458 of a second
1 kilogram = weight of a standard Pt/Ir cylinder
(US copy in Gaithersburg); (still artifact-based unit)
We’ll add moles to this list later.