The Boltzmann constant is the key factor when it comes to redefining the base unit "kelvin" by relating it to a fundamental constant. At the international level, the aim is therefore to determine the numerical value of the Boltzmann constant and to replace the current definition via the triple point of water. Then, also the base unit "kelvin" would no longer depend on a special material property. This, however, requires the Boltzmann constant to be known with a very low uncertainty – so low that it equals the uncertainty of the realization of the triple point of water. To achieve this, scientists worldwide are working on determining the Boltzmann constant in different ways. At PTB, a 
dielectric-constant gas thermometer is used for this purpose in Department 7.4: Temperature (Berlin site).
