In the United States, mass propagation – the seven basic units of the IS – is the responsibility of the National Institute of Standards and Technology (NIST), part of the U.S. Department of Commerce. NIST hosts and maintains America`s official mass standards through 2019. The K20 mass served as the main prototype of the national standard. The other, called K4, served as a “control” standard that monitors the constancy of K20`s mass. And in 1989, the dangers of using human-dependent measurement standards instead of these ultra-precise mathematical standards were vividly illustrated. To the dismay of metrologists around the world, it was discovered that IPK was 50 micrograms lighter than replicas of it that had been distributed worldwide. Since “The Big K” is by definition a kilogram, any change in its mass necessarily changes the definition. Either “The Big K” had lost weight, or the lines had accumulated on the (micro) books. You can just look at it – oh, it`s obviously pounds or kilograms. In an article in Science Advances, they report that manufacturing a new PDK would cost about $45 per kilogram and result in about 86 kilograms of CO2 equivalent per kilogram.
Prior to the redefinition, the kilogram and several other kilogram-based SI units were defined by an artificial metallic artifact: the archival kilogram from 1799 to 1889 and the international prototype kilogram from 1889.  “This redefinition is an important step in scientific progress,” Martin Milton of the International Bureau of Weights and Measures (BIPM) said in a statement. “Using the fundamental constants we observe in nature as the basis for important concepts such as mass and time means that we have a stable foundation from which to advance our scientific understanding, develop new technologies, and address some of society`s greatest challenges.” The replacement of the international prototype of the kilogram as the main standard was motivated by evidence accumulated over a long period of time that the mass of the IPK and its replicas had changed; the IPK had moved about 50 micrograms away from their replicas since their production in the late 19th century. This led to several competing efforts to develop a measurement technique accurate enough to replace the kilogram artifact with a definition based directly on the physical constants of nature.  Standard physical masses such as IPK and its replicas are always used as secondary standards. This definition, the kilogram is in agreement with the old definitions: the mass remains less than 30 ppm of the mass of a liter of water.  Labels estimate the environmental impact of a product from cradle to grave in carbon equivalent, which reflects the greenhouse gas emissions or CO2e emissions consumed during its manufacture, transport, use and end-of-life, measured in grams or kilograms of carbon. The current mass of the kilogram exerts a certain force in Earth`s gravity – in other words, it weighs something.
The revised definition replaces this well-known determination of mechanical force with an electromagnetic measurement related to Planck`s constant and based on electric current and voltage. Using an instrument called kibble balance, according to its inventor Bryan Kibble, an electric current is generated in a coil to create a magnetic field strong enough to balance a mass of one kilogram. The new definition of a kilogram is based on three fundamental constants: the speed of light; the natural microwave radiation of the cesium atom; and Planck`s constant, which describes the size of energy packets that atoms and other particles use to absorb and release energy. On the Earth`s surface, a mass of 1 kg weighs about 2.20 pounds (lbs). Conversely, an object that weighs 1 pound on the Earth`s surface has a mass of about 0.454 kg. There is a qualitative and quantitative difference between kilograms and pounds. Kilograms refer to mass, but pounds refer to weight, the force exerted by a mass against a barrier in the presence of an acceleration field acting perpendicular to the barrier. On the surface of Mars, where gravitational acceleration accounts for 37% of gravitational acceleration, a mass of 1 kg weighs 0.814 lbs. In orbit or in a vehicle traveling in space, the net acceleration is zero and a mass of 1 kg has no weight.
In other words, it is weightless. Unlike watts and joules, however, explicitly electric and magnetic units (volt, ampere…) are not consistent, even in the meter-kilogram-second (absolutely three-dimensional) system. In fact, one can determine which basic units of length and mass must be so that all practical units are consistent (watts and joules, volts, amps, etc.). The values are 107 meters (half of a meridian of the Earth, called quadrant) and 10−11 grams (called eleventh gram [note 11]). [Note 13] In November 2018, the International Committee on Weights and Measures (CIPM) approved a redefinition of SI base units that defines the kilogram by defining Planck`s constant exactly 6.62607015×10−34 kg⋅m2⋅s−1, effectively defining the kilogram in terms of seconds and meters.