is surprisingly close to the average molecular kinetic energy per degree of freedom per kelvin. From these it follows that: 1 kilogram, kg, = 1 joule, J, = 1 watt, W, = 1 J/s = 1 newton, N, = 1 J/m = / 1 pascal, Pa, = 1 N/m2 = /3 1 gray, Gy, = 1 J/kg = / = 1 sievert, Sv, = the ionizing radiation dose equivalent to 1 gray of gamma rays Prior to the revision, between 1889 and 2019, the family of metric (and later SI) units relating to mass, force, and energy were somewhat notoriously defined by the mass of the International Prototype of the Kilogram (IPK), a specific object stored at the headquarters of the International Bureau of Weights and Measures in Paris, meaning that any change to the mass of that object would have resulted in a change to the size of the kilogram and of the many other units whose value at the time depended on that of the kilogram. Temperature From 1954 to 2019, the SI temperature scales were defined using the triple point of water and absolute zero. The 2019 revision replaced these with an assigned value for the Boltzmann constant, k, of J/K, implying: 1 kelvin, K, = J/2 per degree of freedom = per degree of freedom = per degree of freedom Temperature in degrees Celsius, °C, = temperature in kelvins - 273.15 = Amount of substance The mole is an extremely large number of "elementary entities" (i.e. atoms, molecules, ions, etc). From 1969 to 2019, this number was 0.012 × the mass ratio between the IPK and a carbon 12 atom. The 2019 revision simplified this by assigning the Avogadro constant the exact value elementary entities per mole, thus, uniquely among the base units, the mole maintained its independence from the caesium standard: 1 mole, mol, = elementary entities 1 katal, kat, = 1 mol/s = elementary entities/ Electromagnetic units Prior to the revision, the ampere was defined as the current needed to produce a force between 2 parallel wires 1 m apart of 0.2 μN per meter. The 2019 revision replaced this definition by giving the charge on the electron, e, the exact value coulombs. Somewhat incongruously, the coulomb is still considered a derived unit and the ampere a base unit, rather than vice versa. In any case, this convention entailed the following exact relationships between