9. Base unit of thermodynamic temperature.- (1) The base unit of thermodynamic temperature shall be the kelvin. (2) The “kelvin” is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. (3) The kelvin shall also be used for expressing the interval or difference of temperature. (4) Zero degree Celsius corresponds to 273.15 kelvin. (5) The degree Celsius may also be used for expressing the interval or difference of temperature, unit degree Celsius being equal to unit kelvin. | 
