The kelvin, symbol K, is the SI unit of thermodynamic temperature. It is defined by taking the fixed numerical value of the Boltzmann constant k to be 1.380 649 x 10^–23 when expressed in the unit J K^–1, which is equal to kg m² s^–2 K^–1, where the kilogram, metre and second are defined in terms of h, c and Δν_Cs.

The Estonian National Standard Laboratory for Temperature realizes temperature scale
in measuring range (-38.8344 to +419.527) °C, using six temperature fixed-point cells (Hg, H₂0, Ga, In, Sn and Zn)
and a group of standard platinum resistance thermometers with two Precision Thermometry Bridges.

Calibration of thermometers is based on international temperature scale of ITS-90 in the
temperature range of (-196 to +420) °C with the expanded uncertainty of (1 to 80) mK.

Kristjan Tammik
kristjan.tammik@metrosert.ee