The construction of the temperature scale PTB-96 below 15 mK relies mainly on the Curie law of platinum NMR. Therefore the validity of the Curie law is critically reviewed with respect to the properties of platinum including the effect of magnetic impurities and radiation damping. Equipment and procedures are described that were employed to limit potential degradations ot the Curie law. Measurements with other thermometers supporting the NMR results are presented. An uncertainty budget concerning the actual material, instrumentation, and signal processing ist given. PTB-Reihe "Thermodynamik" Band PTB-Th 1weiterlesen