Base SI Units

• Le Systéme Internationale (SI) units are standard in science and technology

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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.