Editing Second (section)

===Atomic definition ===
Even the best mechanical, electric motorized and quartz crystal-based clocks develop discrepancies from environmental conditions; far better for timekeeping is the natural and exact "vibration" in an energized atom. The frequency of vibration (i.e., radiation) is very specific depending on the type of atom and how it is excited.<ref>{{cite book |last1=McCarthy |first1=Dennis D. |author-link1=Dennis McCarthy (scientist) |last2=Seidelmann |first2=P. Kenneth |title=Time: From Earth Rotation to Atomic Physics |chapter = Definition and Role of a Second |year=2009 |location=Weinheim |publisher=Wiley}}</ref> Since 1967, the second has been defined as exactly "the duration of 9,192,631,770 [[frequency|periods]] of the radiation corresponding to the transition between the two [[Hyperfine structure|hyperfine levels]] of the ground state of the [[caesium-133]] atom". This length of a second was selected to correspond exactly to the length of the ephemeris second previously defined. Atomic clocks use such a frequency to measure seconds by counting cycles per second at that frequency. Radiation of this kind is one of the most stable and reproducible phenomena of nature. The current generation of atomic clocks is accurate to within one second in a few hundred million years. Since 1967, atomic clocks based on atoms other than caesium-133 have been developed with increased precision by a factor of 100. Therefore a new definition of the second is planned.<ref name="CGPM2022-Draft">[https://www.bipm.org/documents/20126/64811571/Draft-Resolutions-2022.pdf/2e8e53df-7a14-3fc8-8a04-42dd47df1a04?t=1644502962693 Draft resolutions] of the 27. [[General Conference on Weights and Measures]] in November 2022, Section&nbsp;E, p.&nbsp;25</ref>

Atomic clocks now set the length of a second and the [[time standard]] for the world.<ref name="McCarthy 2009" />{{Rp|231–232}}