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Message: <blockquote data-quote="Aexalon" data-source="post: 7519220" data-attributes="member: 16283">While we're replying to ancient posts: a litre is indeed defined as being a cubic decimeter (meaning that a cubic centimeter is exactly 1 millilitre. However, the current definition of the kilogram is the mass of a reference cylinder of platinum-iridium ("Le Grand K") stored near Paris:[ATTACH]102933[/ATTACH]Sometime next year, this will change when the kilogram will be redefined to derive uniquely from the second, the metre and the Plank constant. Then, the kilogram, like the second and meter will be defined entirely by physical properties of the universe, combined with specifically selected constants:<ul> <li data-xf-list-type="ul">Since 1967, the second s has been defined as exactly 9,192,631,770 times the period of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.</li> <li data-xf-list-type="ul">Since 1983, the metre m has been defined so as to insure that the constant c (<a href="https://en.wikipedia.org/wiki/Speed_of_light" target="_blank">the speed of light in vacuum</a>) is exactly 299,792,458 m / s.</li> <li data-xf-list-type="ul">When adopted (in 2019), the kilogram kg will be defined so as to insure that the constant h (<a href="https://en.wikipedia.org/wiki/Planck_constant" target="_blank">the Planck constant</a>) is exactly 662,607,015 × 10⁻⁴² kg × m² / s.</li> </ul>Of course, those definitions are (will be) the most recent versions of units that were defined by different relations.<ul> <li data-xf-list-type="ul"> a second was defined so that there are 86,400 seconds in a mean solar day of the planet Earth.The approximate actual length of the mean solar day (during the most recent decades) using the modern definition of the second is 86,400.002 seconds. </li> <li data-xf-list-type="ul"> a metre was defined so that there are 40,000,000 metres in a meridian (a circle that passes through both poles) of the planet Earth.The approximate actual length of a great meridian using the modern definition of the metre is 40,007,860 metres. </li> <li data-xf-list-type="ul"> a kilogram was defined as the mass of a cubic decimeter (0.001 m³, or 1 litre) of water at its freezing point.The approximate actual mass of a cubic decimeter of water at 0° C is 0.999841 kilograms, by its current definition ("Le Grand K"). Water is densest at 3.98° C, but even then a cubic decimeter weighs only 0.999973 kilograms. </li> </ul>In summary, Maldin was mostly correct <img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f642.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=":)" title="Smile    :)"  data-smilie="1"data-shortname=":)" /></blockquote>

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