## 7 Great Videos! "New SI"

Part 1: My System of Unitsby Michael de Podesta, NPL

Part 2: The International System of Units

Part 3: The Kilogram Problem

**Veritasium (with NIST) [2017]: How We're Redefining the Kilogram**

**Veritasium (with CSIRO) [2013]: World's Roundest Object**

**NIST [2016]: Measuring Planck's Constant**

**How to Build Your NIST D.I.Y. Watt Balance**

## The New "SI"

**Measurement Science Professionals**

Redefining the (SI) is creating Great
Conversation!

Join the conversation by understanding the changes to come...

## Redefining the International System of Units (SI) in 2018

In the "New SI" four of the SI base units – namely the kilogram, the ampere, the kelvin and the mole – will be redefined in terms of constants; the new definitions will be based on fixed numerical values of the Planck constant (h), the elementary charge (e), the Boltzmann constant (k_{B}), and the Avogadro constant (N_{A}), respectively. Further, the definitions of all seven base units of the SI will also be uniformly expressed using the explicit-constant formulation, and specific mises en pratique will be drawn up to explain the realization of the definitions of each of the base units in a practical way.

**Key to SI Definition Constants:
**Δν = the unperturbed ground state hyperfine transition frequency of the caesium-133 atom ΔνCs is 9,192,631,770 hertz

c = the speed of light in vacuum c is exactly 299,792,458 metres per second

h = the Planck constant h is exactly 6.626 06X x 10

^{–34}joule seconds

e = the elementary charge e is exactly 1.602 17X x 10

^{–19}coulombs

k

_{B}= the Boltzmann constant k is exactly 1.380 6X x 10

^{–23}joules per kelvin

N

_{A}= the Avogadro constant N

_{A}is exactly 6.022 14X x 10

^{23}reciprocal moles

K

_{cd}= the luminous efficacy K

_{cd}of monochromatic radiation of frequency 540 x 10

^{12}Hz is exactly 683 lumens per watt

Note: X represents the yet unknown final digit(s).

## More Information

**Bureau international des poids et mesures (BIPM), France**

European Association of National Metrology Institutes (EURAMET), Europe

**Laboratoire National de Metrologie et D'Essais (LNE), France**

LNE announces outstanding results on the eve of redefining the Kelvin and kilogram units

**National Institute of Standards and Technology (NIST), United States**

SI Redefinition Portal

- Bringing the World Closer to Revised Measurement System, Scientists Update Four Key Fundamental Constants
- New Measurement Will Help Redefine International Unit of Mass
- Universe’s Constants Now Known with Sufficient Certainty to Completely Redefine the International System of Units

National Physical Laboratory (NPL), United Kingdom

CODATA paper outlines changes to four fundamental constants of nature

**Physikalisch-Technische Bundesanstalt (PTB), Germany
**